mmc: pxamci: remove pxa-mmc, gpio-power from devicetree bindings

Devicetree-enabled boards should use proper regulators to control the
power of cards, not GPIOs, so let's remove this property. The regulator
properties are supported by the MMC core and are described in the
generic MMC document:

  Documentation/devicetree/bindings/mmc/mmc.txt

Note that devicetree support for PXA platforms hasn't fully landed yet,
so this binding does not have any users at this point.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>