ARM: dts: msm: add gpio keys support for MSM8917 MTP/CDP/QRD

Add gpio keys support for MSM8917 MTP, CDP and QRD devices.
MTP has vol+, camera focus and camera snapshot, and CDP has
vol+, camera focus, camera snapshot and home keys. While QRD
has only vol+ key.

Change-Id: I2ce68bc8c6f2decf445d3c84a4a23871298bc51a
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>