input: synaptics_fw_update: Add sysfs entry to expose Config ID

Config ID is used to differentiate between different versions of
configuration data on the panel and is needed for debugging.

This patch is a propagated patch from 3.4 kernel
commit - d25bd8cb1b354ce33ecbc2cb5deb61c39a081823,
input: synaptics_fw_update: Add sysfs entry to expose Config ID

Change-Id: Iaa66ff8e328d0480d2e4ce4fc0d9f57434dc7b86
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>