This feature allows calling fsync even if the vfs component is not
used.
The second part of the commit adds an fsync call in the panic test app
enabling it to be used over usb-serial-jtag.
- Added minor improvements to `panic` test app
* Replaced existing API to disable flash cache which did not disabled cache always
(`esp_flash_default_chip->os_func->start(esp_flash_default_chip->os_func_data)`)
with `spi_flash_enable_interrupts_caches_and_other_cpu`
* Included some required headers explicitly (`esp_memory_utils.h` and `esp_heap_caps.h`)