mmc: core: expose info about enhanced rpmb support

Following eMMC JEDEC JESD84-B51 standard, an ehannced form of
rpmb is supported. What this enhanced mode supports is in
addition to be able to write one rpmb or two rpmb frames at a
time, 32 frames can be written at a time.

Expose this information present in ext csd field so that the
user space application that wants to make use of this can do
so.

Change-Id: I53fd962fd7e04b5d2d7804c289d7865c2c5618d5
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>