wil6210: add pm_notify handling

Adding pm_notify to allow the following:
1. Check if suspend is allowed in an earlier stage to prevent
starting the suspend procedure in case it is not allowed
2. Notify the platform driver on the suspend request

Change-Id: Iddacd9b54304b47263647942e1e6784eefb9a6d2
Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Git-commit: e34dc647
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


CRs-Fixed: 1015627
Signed-off-by: Maya Erez <merez@codeaurora.org>