mt76: mt7921: add deep sleep control to runtime-pm knob

Add addtional the deep sleep control to runtime-pm knob to
allow us to control driver switching between the full power
mode and the deep sleep mode the firmware is able to support.

Reviewed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>