mmc: SEND_OP_COND considers card capabilities (voltage)

The first SEND_OP_COND (CMD1) command added is used to ask card capabilities.
After it an AND operation is done between card capabilities and host
capabilities (at the moment only for the voltage field).
Finally the correct value is sent to the MMC, waiting that the card
exits from busy state.

Signed-off-by: Raffaele Recalcati <raffaele.recalcati@bticino.it>
Signed-off-by: Andy Fleming <afleming@freescale.com>