mmc: core: Export API to allow hosts to get the card address

Some hosts controllers, like Cavium, needs to know whether the card
operates in byte- or block-address mode. Therefore export a new API,
mmc_card_is_blockaddr(), which provides this information.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Steven J. Hill <Steven.Hill@cavium.com>
Acked-by: David Daney <david.daney@cavium.com>