msm: restart-header: support multiplatform

Upstream prefers existing drivers be converted to support
multiplatform kernels.  This requires drivers to be located
in generic functionality directories instead of specific
mach directories.

Move restart header to include/soc/qcom/restart.h to support multiplatform
and perform general cleanup.

Change-Id: I125f9ec67f9846919d00c0e0e89867cbb5f71702
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>