mmc: Fixed a problem with old sd or mmc that do not support High speed

As the legacy modes were not added to the list of supported modes, old
cards that do not support other modes could not be used.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>