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

Add gpio keys support for MSMGOLD MTP and CDP devices.
MTP has vol+, camera focus and camera snapshot. While CDP
has vol+, camera focus, camera snapshot and home keys.

Change-Id: Ia2756fb6f8521e9d2d6f8e818e604b61d5ef5ac6
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>