TTY: msm_smd_tty: Clean up includes

msm_smd_tty includes <mach/socinfo.h> but does not use the socinfo API.
msm_smd_tty does use <mach/socinfo.h> as a means to include <linux/of.h>.

Remove the unnecessary socinfo.h include and properly include of.h.

Change-Id: Iddc7a12d42527a7e150600110f6750b044669d14
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>