Panic: mmc: core: implement mmc panic ops

Panic: mmc: core: implement mmc panic ops

BZ: 16578

Port this patch from R2

Ops for panic driver to write kernel logs or user space logs into
eMMC card when panic happened.

Change-Id: I84b9e397bb12610a5a93454a0be63b90a99baccf
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Reviewed-on: http://android.intel.com:8080/26320
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Reviewed-by: Yang, Fei <fei.yang@intel.com>
Tested-by: Sun, Jianhua <jianhua.sun@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>