mmc: sdhci-pxav3: Fix Armada 38x controller's caps according to erratum ERR-7878951

According to erratum 'ERR-7878951' Armada 38x SDHCI controller has
different capabilities than the ones shown in its registers:

- it doesn't support the voltage switching: it can work either with
  3.3V or 1.8V supply
- it doesn't support the SDR104 mode
- SDR50 mode doesn't need tuning

The SDHCI_QUIRK_MISSING_CAPS quirk is used for updating the
capabilities accordingly.

[gregory.clement@free-electrons.com: port from 3.10]

Fixes: 5491ce3f ("mmc: sdhci-pxav3: add support for the Armada 38x SDHCI controller")
Cc: <stable@vger.kernel.org> # v3.15+

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>