input: msg21xx_ts: add support for firmware upgrade

Add sysfs entries to upgrade the firmware from userspace. Update_fw
sysfs entry upgrades the firmware inside the touch controller only
when the controller's firmware version is lesser than that in
userspace's firmware file. Force firmware upgrade sysfs entry
forcefully upgrades the firmware inside the touch controller even
when the controller's firmware version matches that of the firmware
file in userspace.

Change-Id: Ib6046de5230c395b48818d01f26eb9394046808b
Signed-off-by: Mao Li <maol@codeaurora.org>