drivers: soc: qcom: Add snapshot of virtual subsystem notification driver

This is a snapshot of the virtual subsystem notification driver
as of msm-4.4 commit <36e8e9585f4b10> (soc: qcom:
subsystem_notif_virt: Only initialize work for virtual systems).

Change-Id: Ic8bb9ac740d0590432ad8f9ec1a131299b22831a
Signed-off-by: Anant Goel <anantg@codeaurora.org>