mmc: add a sysfs entry to show write reliability

mmc: add a sysfs entry to show write reliability

BZ: 24365

add a sysfs rel_set in /sys/block/mmcblk0/device/ to show the
write reliability.
If bit0 of rel_set is 1, then write reliability for user data
area is enabled.

Change-Id: I02700b7597499d5660b4ee46a781f6c2bb002b88
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Reviewed-on: http://android.intel.com:8080/35851
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>