These definitions have ended up being chip specific. Moving them into
respective soc_memory_layout.c makes the whole picture of memory
regions easier to see, and also makes adding support for new chips
easier.
1. add brownout detector HAL for esp32 and esp32s2
2. enable brownout reset for esp32 rev. 1 and above
3. add approximate brownout detector levels for esp32s2
test_mux register doesn't exist in RTCCNTL anymore, remove it from
struct header. Also remove adc_ll_vref_output implementation, which
depends on that register.
