drivers: soc: qcom: handle system sleep activities

When all the CPUs in the Apps processor subsystem
are powered off, the system may also reduce its
bandwidth and shared resource requirements.

The resource requests are sent through the SMD
from APSS subsystem. The sleep requests also need
to be written to the rpm to save power. This driver
handles the last few steps when entering system sleep.

When notified, the next wakeup timer value is written
to the MPM to be setup in the always-on domain timer.

Change-Id: Iab9e38d602d4f84e506471ec0864d2c6fb550b42
Signed-off-by: Raghavendra Kakarla <rkakarla@codeaurora.org>