doc: update the memory types and startup docs

docs/en/api-reference/system/mem_alloc.rst

@@ -92,6 +92,10 @@ DMA-Capable Memory
 
 Use the ``MALLOC_CAP_DMA`` flag to allocate memory which is suitable for use with hardware DMA engines (for example SPI and I2S). This capability flag excludes any external PSRAM.
 
+.. only SOC_SPIRAM_SUPPORTED and not esp32::
+
+    The EDMA hardware feature allows DMA buffers to be placed in external PSRAM, but there may be additional alignment constraints. Consult the {IDF_TARGET_NAME} Technical Reference Manual for details. To allocate a DMA-capable external memory buffer, use the ``MALLOC_CAP_SPIRAM`` capabilities flag together with :cpp:func:`heap_caps_aligned_alloc` with the necessary alignment specified.
+
 .. _32-bit accessible memory:
 
 32-Bit Accessible Memory

docs/en/api-reference/system/system.rst

@@ -153,6 +153,8 @@ To get the version at build time, additional version macros are provided. They c
       #endif
 
 
+.. _app-version:
+
 App version
 -----------
 Application version is stored in :cpp:class:`esp_app_desc_t` structure. It is located in DROM sector and has a fixed offset from the beginning of the binary file.