mmc: sdhci: dt: Add device tree properties sdhci-caps and sdhci-caps-mask

On some systems the sdhci capabilty register is incorrect for one
reason or another.

The sdhci-caps-mask property specifies which bits in the register
are incorrect and should be turned off before using sdhci-caps to turn
on bits.

The sdhci-caps property specifies which bits should be turned on.
Signed-off-by: Zach Brown <zach.brown@ni.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/sdhci.txt

+The properties specific for SD host controllers. For properties shared by MMC
+host controllers refer to the mmc[1] bindings.
+
+  [1] Documentation/devicetree/bindings/mmc/mmc.txt
+
+Optional properties:
+- sdhci-caps-mask: The sdhci capabilities register is incorrect. This 64bit
+  property corresponds to the bits in the sdhci capabilty register. If the bit
+  is on in the mask then the bit is incorrect in the register and should be
+  turned off, before applying sdhci-caps.
+- sdhci-caps: The sdhci capabilities register is incorrect. This 64bit
+  property corresponds to the bits in the sdhci capability register. If the
+  bit is on in the property then the bit should be turned on.