RxAGC

The RxAGC loop ensures constant power to demod， and keeps ADC from
saturating by changing receiver gain based on signal strength.
The purpose of the DVGA offset is to adjust the overall DVGA gain by a
constant amount so that the RSSI represented by AGC_VALUE matches
true Rx power at the antenna connector, particularly when the LNA is in its
highest gain state.
RFSW is responsible for reading NV items for band and loading
frequency-compensated DVGA and LNA offset values into hardware
registers.
All RF and FE-related programming is doneby RFSW via the new RFLM/FED.
RxAGC updates are done periodically and involve:
1. Firmware runs the AGC loops and calculates the AGC based on RSSI. At each
Rx slot, the firmware provides RFLM with the AGC value, the LNA state, and an
action time.
2. RFLM is responsible for programming RFFE and baseband configuration.