msm: spm: Support RPM handshake control bit in SPM

SAW2 3.0 supports RPM handshake using SAW2_SPM_CTL register for the
sleep command in the SPM sequence. This allows a single power collapse
sequence for both cases when we don't want to notify RPM on apps power
down and when we want to.

This implementation is the same across all IPs in the apps processor
subsystem, but only a few SAW modules are allowed to notify RPM and
handshake with RPM when executing the 0x03 sleep command. Disallow and
check incorrect call on SPM, based on the flag provided in the device
tree.

Based on this flag in DT, set the SLP_CMD_MODE bit in SPM_CTL
register. Fail to set the low power mode if we are trying to send
rpm notification for a mode that does not support rpm notification.

Change-Id: I5527bd8da62673d68867842dbd80000d67965e6a
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>