[MMC] Provide access to Samsung's e-MMC Smart Report via sysfs

Added CONFIG_MMC_SAMSUNG_SMART which enables code that will
expose Samsung's proprietary e-MMC health information to sysfs.

Example output:
$ cat /sys/devices/platform/*/*/mmc_host/mmc*/mmc*/samsung_smart
version                       : 0
error mode                    : Normal
super block size              : 4194304
super page size               : 32768
optimal write size            : 32768
read reclaim count            : 0
optimal trim size             : 262144
number of banks               : 2
initial bad blocks per bank   : 10,4,0,0
runtime bad blocks per bank   : 0,0,0,0
reserved blocks left per bank : 131,137,0,0
all erase counts (min,avg,max): 0,760,65535
SLC erase counts (min,avg,max): 0,5,74
MLC erase counts (min,avg,max): 0,790,65535

Change-Id: Ib476ea5d35264aa94b378f49121d31b20b751f04
Signed-off-by: Scott Anderson <saa@android.com>