dt-bindings: mmci: add stm32 sdmmc variant

This patch adds properties for stm32 sdmmc variant.
Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/mmci.txt

@@ -16,8 +16,10 @@ Optional properties:
 - arm,primecell-periphid : contains the PrimeCell Peripheral ID, it overrides
                            the ID provided by the HW
 - resets                 : phandle to internal reset line.
+			   Should be defined for sdmmc variant.
 - vqmmc-supply           : phandle to the regulator device tree node, mentioned
                            as the VCCQ/VDD_IO supply in the eMMC/SD specs.
+specific for ux500 variant:
 - st,sig-dir-dat0        : bus signal direction pin used for DAT[0].
 - st,sig-dir-dat2        : bus signal direction pin used for DAT[2].
 - st,sig-dir-dat31       : bus signal direction pin used for DAT[3] and DAT[1].
@@ -25,6 +27,14 @@ Optional properties:
 - st,sig-dir-cmd         : cmd signal direction pin used for CMD.
 - st,sig-pin-fbclk       : feedback clock signal pin used.
 
+specific for sdmmc variant:
+- st,sig-dir             : signal direction polarity used for cmd, dat0 dat123.
+- st,neg-edge            : data & command phase relation, generated on
+                           sd clock falling edge.
+- st,use-ckin            : use ckin pin from an external driver to sample
+                           the receive data (example: with voltage
+			   switch transceiver).
+
 Deprecated properties:
 - mmc-cap-mmc-highspeed  : indicates whether MMC is high speed capable.
 - mmc-cap-sd-highspeed   : indicates whether SD is high speed capable.