rtw88: not to control LPS by each vif

The original design of LPS enter/leave routines allows
to control the LPS state by each interface. But the
hardware cannot actually handle it that way. This means
the hardware can only enter LPS once with an associated
port, so there is no need to keep tracking the state of
each vif.

Hence the logic of enter/leave LPS state can be simple,
just to check the state of the device's flag. And for
leaving LPS state, it will get the same port id to send
to inform the hardware.

Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>