mmc: core: Add the ability to enable BKOPS

If the card and the host support BKOPS, and BKOPS is not enabled
yet, set the BKOPS_EN bit to enable BKOPS.
This bit is one time programmable.

Change-Id: I9211f68cf7a6ba7e57964a5acb908efa9a9e515a
Signed-off-by: Maya Erez <merez@codeaurora.org>