Merge branch 'bugfix/rtc_reg_fields' into 'master'

soc: allow REG_SET_FIELD to be used for bit fields

- Fixes an issue with `rtc_clk_apll_enable`: https://esp32.com/viewtopic.php?f=13&t=1673
- Fixes `rtc_clk_fast_freq_set` function always selecting XTAL/4 as fast clock source.
- Fixes regression in deep sleep current (7uA instead of 5uA).

See merge request !674