msm: board-msm7x27: Remove platform devices for USB functions

With the new USB composite framework, USB functions need
not to be registered as platform devices.
Register only android_composite device as platform device
which is used to pass update_pid_serial_number function
callback used by DIAG.

Change-Id: Iedfdd46999f2063c42e4744afa75214ce4b7271e
Signed-off-by: Pankaj Kumar <pakuma@codeaurora.org>
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>