Commit 3a48edc4 ("mmc: sdhci: Use mmc core regulator infrastucture")
changed the behavior for how to assign the ocr_avail mask for the mmc
host. More precisely it started to mask the bits instead of assigning
them.

Restore the behavior, but also make it clear that an OCR mask created
from an external regulator overrides the other ones. The OCR mask is
determined by one of the following with this priority:

1. Supported ranges of external regulator if one supplies VDD
2. Host OCR mask if set by the driver (based on DT properties)
3. The capabilities reported by the controller itself

Fixes: 3a48edc4 ("mmc: sdhci: Use mmc core regulator infrastucture")
Cc: Tim Kryger <tim.kryger@gmail.com>
Reported-by: Yangbo Lu <yangbo.lu@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Tim Kryger <tim.kryger@gmail.com>