ath10k: refactor suspend/resume functions

Suspend/resume callbacks are not protected by configuration mutex
so adding such protection. Also in order to simplify implemetation
of suspend function wait queue is replaced by completion.

Signed-off-by: Marek Puzyniak <marek.puzyniak@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>