GPIO-KEYS: combine two gpio-keys devices into one

GPIO-KEYS: combine two gpio-keys devices into one

BZ: 20893

There are currently two "gpio-keys" platform devices defined in the
kernel with the same string name, one is in blackbay_pr2.c and the
other in mrst.c. This is causing problem when registering the second
one. Solution is to combine them into one platform device.

Change-Id: I83385db305f68e59c7878aed46b5defd66ec9d8e
Signed-off-by: Fei Yang <fei.yang@intel.com>
Reviewed-on: http://android.intel.com:8080/32692
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Reviewed-by: Kuppuswamy, Sathyanarayanan <sathyanarayanan.kuppuswamy@intel.com>
Tested-by: Ng, Cheon-woei <cheon-woei.ng@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>