mmc: dt: Consolidate DT bindings

This patch unifies the current DT MMC bindings documentation and code,
adds generic MMC DT bindings documentation, and updates .dts files for
consistency.

[cjb: typo fixes, addition of max-frequency property]
Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/arch/arm/boot/dts/imx6q-arm2.dts b/arch/arm/boot/dts/imx6q-arm2.dts
index ce1c823..d2eaf52 100644
--- a/arch/arm/boot/dts/imx6q-arm2.dts
+++ b/arch/arm/boot/dts/imx6q-arm2.dts
@@ -41,7 +41,7 @@
 			};
 
 			usdhc@0219c000 { /* uSDHC4 */
-				fsl,card-wired;
+				non-removable;
 				vmmc-supply = <&reg_3p3v>;
 				status = "okay";
 			};