wl12xx: Add Support for Low Power DRPw (LPD) Mode

The Low Power DRPw (LPD) mode contains several optimizations
that designed to reduce power consumption. The purpose
is to save current consumption in RX and Listen mode.

LPD setting apply only for wl127x AP mode (not wl128x)

Signed-off-by: Shahar Levi <shahar_levi@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>