soc: qcom: mem-offline: Add support for QMP mailbox communication

Add support in mem offline driver to request that memory be physically
onlined and offlined when it is logically onlined and offlined.

Change-Id: I3a792deb6ae0c43bae9453827071f899cfc2fc05
Signed-off-by: Liam Mark <lmark@codeaurora.org>