ARM: dts: msm: add DT node for GPIO keys on MSMTITANIUM

Add gpio based keys device node to MSMTITANIUM. The supported
keys are VOLUME UP, CAMERA SNAPSHOT, CAMERA FOCUS for both
CDP and MTP and HOME KEY only for CDP.

Change-Id: Ic614e2bf48948257a04226560844e4ef2ad4459a
Signed-off-by: Abinaya P <abinayap@codeaurora.org>