msm: ipa: add support for AP suspend in ipa driver

When AP suspend is triggered, IPA driver checks whether there are active
clients of IPA. In case there are active clients, postpone the AP suspend
operation for a later time.

Change-Id: Ib00d07c3fa93492aa532bff5b23d93ca557de2ca
Signed-off-by: Gidon Studinski <gidons@codeaurora.org>