msm: ipa: disable IPA clock gating from debugfs

IPA clock gating is enabled by default.
Add the ability to dynamically enable and disable
IPA clock gating from debugfs.

Disable IPA clock gating:
	echo 1 > /sys/kernel/debug/ipa/keep_awake
Enable IPA clock gating:
	echo 0 > /sys/kernel/debug/ipa/keep_awake

Change-Id: I4ebe146d2d4c918674fbf70cbddbe6b252e024d7
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Ravit Katzav <rkatzav@codeaurora.org>