This change ensure the MMC card is in Identification Mode.
The card might be in Data Transfer Mode if a pre UEFI Boot Loader
had initialized the card.
A potential optimization would be to skip the Identification Mode
in this case.
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13872 6f19259b-4bc3-4df7-8a09-765794883524