dt-bindings: mmc: exynos-dw-mshc: Add support for ARTPEC-8

The ARTPEC-8 SoC has a DWMMC controller that is compatible with the
Exynos 7 version v2.70a. The main differences from Exynos 7 is that it
does not support HS400 and has extended data read timeout.

Add compatibility string "axis,artpec8-dw-mshc" for ARTPEC-8.
Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211220113026.21129-2-marten.lindahl@axis.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/exynos-dw-mshc.txt

@@ -22,6 +22,8 @@ Required Properties:
 	  specific extensions.
 	- "samsung,exynos7-dw-mshc-smu": for controllers with Samsung Exynos7
 	  specific extensions having an SMU.
+	- "axis,artpec8-dw-mshc": for controllers with ARTPEC-8 specific
+	  extensions.
 
 * samsung,dw-mshc-ciu-div: Specifies the divider value for the card interface
   unit (ciu) clock. This property is applicable only for Exynos5 SoC's and