MMC: Consolidate voltage definitions

Consolidate the list of available voltages.

Up until now, a separate set of defines has been
used for host->vdd than that used for the OCR
voltage mask values. Having two sets of defines
allows them to get out of sync and the current
sets are already inconsistent with one claiming
to describe ranges and the other specific voltages.

Only the SDHCI driver uses the host->vdd defines and
it is easily fixed to use the OCR defines.

Signed-off-by: Philip Langdale <philipl@overt.org>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>