refactor(gpio): public some IO configuration functions

This allows different peripheral drivers to act on the same IO.

docs/en/api-reference/peripherals/pcnt.rst

@@ -87,7 +87,6 @@ To install a PCNT channel, you must initialize a :cpp:type:`pcnt_chan_config_t`
 - :cpp:member:`pcnt_chan_config_t::edge_gpio_num` and :cpp:member:`pcnt_chan_config_t::level_gpio_num` specify the GPIO numbers used by **edge** type signal and **level** type signal. Please note, either of them can be assigned to ``-1`` if it is not actually used, and thus it will become a **virtual IO**. For some simple pulse counting applications where one of the level/edge signals is fixed (i.e., never changes), you can reclaim a GPIO by setting the signal as a virtual IO on channel allocation. Setting the level/edge signal as a virtual IO causes that signal to be internally routed to a fixed High/Low logic level, thus allowing you to save a GPIO for other purposes.
 - :cpp:member:`pcnt_chan_config_t::virt_edge_io_level` and :cpp:member:`pcnt_chan_config_t::virt_level_io_level` specify the virtual IO level for **edge** and **level** input signal, to ensure a deterministic state for such control signal. Please note, they are only valid when either :cpp:member:`pcnt_chan_config_t::edge_gpio_num` or :cpp:member:`pcnt_chan_config_t::level_gpio_num` is assigned to ``-1``.
 - :cpp:member:`pcnt_chan_config_t::invert_edge_input` and :cpp:member:`pcnt_chan_config_t::invert_level_input` are used to decide whether to invert the input signals before they going into PCNT hardware. The invert is done by GPIO matrix instead of PCNT hardware.
-- :cpp:member:`pcnt_chan_config_t::io_loop_back` is for debug only, which enables both the GPIO's input and output paths. This can help to simulate the pulse signals by function :cpp:func:`gpio_set_level` on the same GPIO.
 
 Channel allocating and initialization is done by calling a function :cpp:func:`pcnt_new_channel` with the above :cpp:type:`pcnt_chan_config_t` as an input parameter plus a PCNT unit handle returned from :cpp:func:`pcnt_new_unit`. This function will return a PCNT channel handle if it runs correctly. Specifically, when there are no more free PCNT channel within the unit (i.e., channel resources have been used up), then this function will return :c:macro:`ESP_ERR_NOT_FOUND` error. The total number of available PCNT channels within the unit is recorded by :c:macro:`SOC_PCNT_CHANNELS_PER_UNIT` for reference. Note that, when install a PCNT channel for a specific unit, one should ensure the unit is in the init state, otherwise this function will return :c:macro:`ESP_ERR_INVALID_STATE` error.
 
@@ -247,7 +246,6 @@ This function should be called when the unit is in the init state. Otherwise, it
 
         -  :cpp:member:`pcnt_clear_signal_config_t::clear_signal_gpio_num` specify the GPIO numbers used by **clear** signal. The default active level is high, and the input mode is pull-down enabled.
         -  :cpp:member:`pcnt_clear_signal_config_t::invert_clear_signal` is used to decide whether to invert the input signal before it going into PCNT hardware. The invert is done by GPIO matrix instead of PCNT hardware. The input mode is pull-up enabled when the input signal is inverted.
-        -  :cpp:member:`pcnt_clear_signal_config_t::io_loop_back` is for debug only, which enables both the GPIO's input and output paths. This can help to simulate the clear signal by function :cpp:func:`gpio_set_level` for the same GPIO.
 
     This signal acts in the same way as calling :cpp:func:`pcnt_unit_clear_count`, but is not subject to software latency, and is suitable for use in situations with low latency requirements. Also please note, the flip frequency of this signal can not be too high.