mmc: panic_ops: fix emmc write when in kernel panic mode

mmc: panic_ops: fix emmc write when in kernel panic mode

BZ: 33786

CLV cannot save kernel panic log and logcat log after kernel happened.
It because eMMC card has switched to DDR mode but host is still in DDR
mode after kenel panic happens. So change eMMC card to SDR mode only after
kernel panic happened.

Change-Id: I40768128598fc2a4afdeb341837da360997d50f7
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Reviewed-on: http://android.intel.com:8080/47372
Reviewed-by: Tang, Richard <richard.tang@intel.com>
Tested-by: Sun, Jianhua <jianhua.sun@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>