ath6kl: add suspend_cutpower module parameter

This is to force ath6kl to power off hardware during suspend even if
sdio support keep power. This is needed, for example, when sdio
controller is buggy or maximum powersaving is desired.

Usage:

insmod ath6kl.ko suspend_cutpower=1

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>