input: synaptic_dsx: add sysfs entry for force firmware update

firmware update method compare the version id and package id
the of new firmware with the existing firmware of the touch controller.
if the version id of the new firmware is older than the existing firmware
it will skip the firmware update. sometime to measure the touch performance
difference between the new firmware and old firmware we need to update
old firmware in touch controller. So this sysfs entry bypass the firmware
header check before the firmware update and allow the driver to update
the old firmware in the touch controller.

Change-Id: Ib4f5b75940c54c4d04ac1701d387d59f50eb3a71
Signed-off-by: Sarada Prasanna Garnayak <c_sgarna@codeaurora.org>