msm: boot_stats: Support multiplatform

Convert to support multiplatform kernels. This requires drivers to be
located in generic functionality directories instead of specific mach
directories.

Move over the boot stats driver to drivers/soc/qcom/boot_stats.c from
arch/arm/mach-msm/boot_stats.c

Change-Id: Iee7ec288fe44606b468dc533bb4221f8d018b3cb
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>