Input: cyapa - add gen3 trackpad device firmware update support

Add support for firmware image update for gen3 trackpad devices; the
firmware update is initiated by writing to update_fw sysfs attribute.

Signed-off-by: Dudley Du <dudl@cypress.com>
Tested-by: Jeremiah Mahler <jmmahler@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>