wl12xx: remove PS management code

Removal of PS management code from the driver as PS
is handled by the FW (dynamic PS)

Signed-off-by: Eyal Shapira <eyal@wizery.com>
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>