mmc: dw_mmc: Power on vqmmc in MMC_POWER_ON, not MMC_POWER_UP

If we power up vqmmc in MMC_POWER_ON then we end up turning it on
before mmc_power_up() sets the signal voltage.  That's not so great
since we might be powering it up at the wrong voltage.

Note that this is how Yuvaraj originally coded things up in
<https://patchwork.kernel.org/patch/4401231/

> but he changed it on my
suggestion.  Apparently I was wrong.

Reported-by: Alexandru M Stan <amstan@chromium.org>
Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>