input: atmel_mxt_ts: Add support for keyarray object

Keyarray(T15) object is used for handling capactive keys.
It can handle 32 keys and the keys supported are passed
from platform data as key_codes.

Change-Id: Iac589afb59e8ff69b6e1eb86bafdc0b5382c3edd
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>