input: atmel_mxt_ts: Support hex format firmware upgrade

The firmware file from Atmel is in hex format, while the touch
controller expects binary data. The driver converts the data from
hex to binary before passing them to the controller for upgrade.

Change-Id: Iedccf467f18d3156280396153d7ca7cef1a52afb
Signed-off-by: Jing Lin <jinglin@codeaurora.org>