input: touchscreen: Add force fw_update support via sysfs entry

Add sysfs entry for force fw_update support in Goodix
driver.
Change the usage of kstrtoul to sscanf in driver to avoid
portability issues.

CRs-fixed: 579806
Change-Id: I147a3e465170dda7af415ade29c04257d9b11a6b
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>