rtc: as3722: add shutdown support

rtc: as3722: add shutdown support

When shutdown process is ongoing, dont allow rtc
read/write/irq activity.Add shutdown hook to the
driver to disable irq and cancel any pending
irq_work

Bug 200072946

Change-Id: I1a68d17ec49ee32e849ad965a144b84be19ba6c5
Signed-off-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-on: http://git-master/r/677751
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Venkat Moganty <vmoganty@nvidia.com>
Reviewed-by: Matthew Pedro <mapedro@nvidia.com>