mmc: host: Add speed class in debugfs

mmc: host: Add speed class in debugfs

Add support in debugfs to identify speed class of
SD cards.

Bug 2420580

Change-Id: I9f869aa639f5acec80bea5ba56b82974e96a7a91
Signed-off-by: Aniruddha Rao <anrao@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1928864
(cherry picked from commit b4c433d578faff4eb72451a444fd9dfc27489041)
Reviewed-on: https://git-master.nvidia.com/r/1932065
GVS: Gerrit_Virtual_Submit
Reviewed-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>