msm: devices-8960: Add a rpmrs level to support SVS voltage

This commit includes a few updates to support voting for SVS voltage.
1) Update the active voltage to include the SVS voltage as the system
is functional in the SVS voltage.
2) When interrupts not monitored by MPM are enabled, disallow modes
whose the upper bound vdd_dig is lesser than Retention high voltage.
3) Handle vdd_dig and vdd_mem edge cases to allow modes when the voted
voltage is equal to upper threshold.

Change-Id: Idebdf4d8be8d9a2aa741b7219ae31ab0e2a9b165
Signed-off-by: Maheshkumar Sivasubramanian <msivasub@codeaurora.org>