drivers: soc: qcom: idle: Snapshot of spm driver as of msm-4.4

This is a snapshot of the SPM driver functionality as of
8992f7dd089 on msm-4.4 branch

Checkpatch issues were resolved
	- BUG_ON() have been removed.
	- Comments around mb, wmb
	- Return -ENODEV instead of -ENOSYS
	- Whitespace issues, Line over 80 chars etc

Change-Id: I73b020214fdcc7eb695cf8f5b52cf7885a0a10cd
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>