System: fix RTCFAST section alignment
System: fix RTCFAST section alignment

This bugfix contains 3 fixes:
1. .rtc_dummy section is removed (not needed for C3)
2. .rtc_text section is padded with 16B for possible CPU prefetch
3. .rtc_text section is aligned to 4B boundary to comply with PMS Memprot requirements

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf