dt-bindings: mmc: mmci: Add st,stm32-sdmmc2 compatible

Although this compatible is not used in kernel, as we use the common
MMCI driver, it is used by bootloaders. The U-Boot driver was merged
before the kernel driver and uses this compatible.

To avoid issues when aligning device tree files between kernel and
boot loader, the ST dedicated compatible is added to bindings file.
Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211210091834.28958-1-yann.gautier@foss.st.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

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

@@ -53,6 +53,12 @@ properties:
         items:
           - const: arm,pl18x
           - const: arm,primecell
+      - description: Entry for STMicroelectronics variant of PL18x.
+          This dedicated compatible is used by bootloaders.
+        items:
+          - const: st,stm32-sdmmc2
+          - const: arm,pl18x
+          - const: arm,primecell
 
   clocks:
     description: One or two clocks, the "apb_pclk" and the "MCLK"