msm: Adds sync.h and sw_sync.h to Kbuild file

The sync.h and sw_sync.h header files were not added into the Kbuild and
thus were not included in kernel header build. This change adds the
files to the Kbuild file so that they will now properly appear in
userspace api header builds.

Change-Id: I83960d6832a8a91a98daf505a2bed1207c696c55
CRs-Fixed: 1023357
Signed-off-by: Glenn Stroz <gstroz@codeaurora.org>