mmc: mmci: Add bindings to operate CMD, CK, CKIN pins as GPIO

Add DT bindings to describe GPIO line associated with CMD, CK, CKIN pins.
Signed-off-by: NMarek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Ludovic Barre <ludovic.barre@st.com>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210124170258.32862-1-marex@denx.deSigned-off-by: NUlf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/arm,pl18x.yaml

@@ -127,6 +127,26 @@ properties:
       driver to sample the receive data (for example with a voltage switch
       transceiver).
 
+  st,cmd-gpios:
+    maxItems: 1
+    description:
+      The GPIO matching the CMD pin.
+
+  st,ck-gpios:
+    maxItems: 1
+    description:
+      The GPIO matching the CK pin.
+
+  st,ckin-gpios:
+    maxItems: 1
+    description:
+      The GPIO matching the CKIN pin.
+
+dependencies:
+  st,cmd-gpios: [ "st,use-ckin" ]
+  st,ck-gpios: [ "st,use-ckin" ]
+  st,ckin-gpios: [ "st,use-ckin" ]
+
 unevaluatedProperties: false
 
 required: