input: atmel_mxt_ts: Add support for object PROCI_SHIELDLESS_T56

The mXT1386E touch controller supports a new signal processing object
PROCI_SHIELDLESS_T56. This object is both readable and writable.

Change-Id: I418df8c3f05dc5265a1e7581d9c7e654a9fd3c4c
Signed-off-by: Jing Lin <jinglin@codeaurora.org>