powerpc: add mmc-spi-slot bindings

The bindings describes a case where MMC/SD/SDIO slot directly connected to
a SPI bus.  Such setups are widely used on embedded PowerPC boards.

The patch also adds the mmc-spi-slot entry to the OpenFirmware modalias
table.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Cc: David Brownell <david-b@pacbell.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Kumar Gala <galak@gate.crashing.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/powerpc/dts-bindings/mmc-spi-slot.txt

@@ -0,0 +1,23 @@
+MMC/SD/SDIO slot directly connected to a SPI bus
+
+Required properties:
+- compatible : should be "mmc-spi-slot".
+- reg : should specify SPI address (chip-select number).
+- spi-max-frequency : maximum frequency for this device (Hz).
+- voltage-ranges : two cells are required, first cell specifies minimum
+  slot voltage (mV), second cell specifies maximum slot voltage (mV).
+  Several ranges could be specified.
+- gpios : (optional) may specify GPIOs in this order: Card-Detect GPIO,
+  Write-Protect GPIO.
+
+Example:
+
+	mmc-slot@0 {
+		compatible = "fsl,mpc8323rdb-mmc-slot",
+			     "mmc-spi-slot";
+		reg = <0>;
+		gpios = <&qe_pio_d 14 1
+			 &qe_pio_d 15 0>;
+		voltage-ranges = <3300 3300>;
+		spi-max-frequency = <50000000>;
+	};