In esp32c2 and esp32c61 memory_layout.c files, the config used to allow
MALLOC_CAP_EXEC was CONFIG_ESP_SYSTEM_MEMPROT_FEATURE when
CONFIG_ESP_SYSTEM_PMP_IDRAM_SPLIT should be used.
Closes https://github.com/espressif/esp-idf/issues/14836
1. move startup_stack attr from soc_memory_type_desc_t to soc_memory_region_t and
remove unused aliased_iram field
2. all of the last level of RAM is retention dma accessible on esp32c3
3. remove esp32c2 and later chips retention dma accessible memory caps
4. allow allocate memory from RTC_RAM with MALLOC_CAP_EXEC cap