input: atmel_maxtouch_ts: fix firmware update routines

Fix firmware and configuration update routines to follow
device specification. Parse the firmware and configuration
file names from DT and provide interfaces to read them
from user space.

Change-Id: I9fa2a13a17702cd26d36987a6584adf398e962a8
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>