mt76: mt7921: Let PCI core handle power state and use pm_sleep_ptr()

PCI power state and wakeup are already handled by PCI core, so it's not
necessary to handle them in the driver.

Also switch to use pm_sleep_ptr() to remove #ifdef guard.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>