input: touchscreen: atmel_mxt_ts - orientation and size

Change the touch orientation in the device-tree file.
Support a small clipped valid region to be used.

Change-Id: Ib2cd32187fa11b8d6e5f37f5ede8ab8d62465420
Signed-off-by: Fei Mao <feim1@codeaurora.org>