touchscreen: add suspend hooks to synaptics_i2c_rmi

touchscreen driver currently has no kernel-based suspend hooks.
this is causing very high battery drain due to it always being active.
(in calls, while in the pocket, etc)

this patch ports the framebuffer suspend hook from the generic
synaptics_i2c_rmi4 driver in drivers/input/touchscreen.

Change-Id: Iaf7d2d7db2773f8ced25b78f940bf38b78d0daaf

Patchset: 1
http://review.cyanogenmod.org/#/c/56805/