mmc: check if mmc cards < 2GB do sector addressing

Some TOSHIBA MMC cards only support sector addressing even though the
size is < 2GB.  According to JEDEC Spec JESD84-A441-1 the ocr register
(bits 30, 29) determine byte/sector mode.  Use them.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>