msm: smd_tty: Remove incorrect use of smd_private.h

smd_private.h is an internal header file used to share private internal
details of the SMD driver to related components for the purposes of
debugging, segregating functionality, etc.  Nothing in smd_private.h
is intended to be exposed for client use, and including it in a file
should be a special exception, not a normal usecase.

No private internal details have to be accessed by the smd_tty driver,
so substitute the corresponding public api headers where smd_private.h is
used.

Change-Id: I682bea3782d141194ac7aee00ea45232f7f47a27
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>