soc: qcom: add subsystem_restart.h header file

This is a snapshot of include/soc/qcom/subsystem_restart.h as of
msm-3.10 commit

acdce027751d5a7488b283f0ce3111f873a5816d (Merge "defconfig: arm64: Enable
ONESHOT_SYNC for msm8994")

The core subsystem restart functionality is not added, however, this
file is necessary to allow SMD to build.

Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>