soc: qcom: mem-offline: Dynamic Memory Region Offline driver

Add support for DDR Self-Refresh power management through the dynamic
memory offline framework. This driver interfaces between the memory
hotplug subsystem and AOP which hot adds or removes memory blocks and
controls the start/stop of self-refresh of these DDR regions. This
helps reduce power consumption during idle mode of the system.

The driver listens to memory hotplug notifications and requests AOP
to start DDR self-refresh after the memory block is hot-added and
stops refresh after memory block is hot-removed.

The driver also adds /sys/kernel/mem-offline directory node to give
stats about each of the memory block.

Change-Id: I33292130236cefb79794740d6f2bdc187b7cbca8
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
[swatsrid@codeaurora.org: Fix merge conflicts and trivial warnings]
Signed-off-by: Swathi Sridhar <swatsrid@codeaurora.org>