input: atmel-mxt-ts: Provide firmware name via platform data

This allows firmware upgrade only when a firmware name is provided.
The platform data (config data) of the latest firmware will point
to a NULL string which prevents auto firmware upgrade at boot
(if enabled by the userspace).

Change-Id: Ifef57a9dab9306cf4f1fe7a6c7e52c5e92a25d4a
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>