mmc: core: Determine correct access mode for eMMC cards by reading OCR

MMC core reads SEC_COUNT information from EXT_CSD register and assumes
that the card supports sector access mode. Some eMMC cards (<=2GB) do not
support this mode even though they have SEC_COUNT value defined, causing
failure while populating extended partitions. Sector/Byte access mode
information is stored in OCR register. Hence, read OCR bit 30 and then
confirm it with SEC_COUNT value to know  whether the card supports sector
access mode or byte access mode.

Change-Id: Ifdfff35309e8667cd2c2ac2761b9a708d5b785d3
Signed-off-by: Sujith Reddy Thumma <sthumma@codeaurora.org>