wifi: mt76: mt7921s: Switch to DEFINE_SIMPLE_DEV_PM_OPS() and pm_sleep_ptr()

Use the new DEFINE_SIMPLE_DEV_PM_OPS() and pm_sleep_ptr() macros to
handle the .suspend/.resume callbacks. The new macros allow suspend
and resume functions to be automatically dropped without any #ifdef
guards.

Tested-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>