mmc: sdhci: Use mmc core regulator infrastucture

Switch the common SDHCI code over to use mmc_host's regulator pointers
and remove the ones in the sdhci_host structure.  Additionally, use the
common mmc_regulator_get_supply function to get the regulators and set
the ocr_avail mask.

This change sets the ocr_avail directly based upon the voltage ranges
supported which ensures ocr_avail is set correctly while allowing the
use of regulators that can't provide exactly 1.8v, 3.0v, or 3.3v.

Signed-off-by: Tim Kryger <tim.kryger@gmail.com>
Signed-off-by: Markus Mayer <markus.mayer@linaro.org>
Reviewed-by: Matt Porter <mporter@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>