arm: dts: u8500: u-boot: Add fixed clock for eMMC

So far there is no need for a clock driver in U-Boot because the
previous boot stage leaves all the necessary clocks on. However,
some drivers in U-Boot (e.g. arm_pl180_mmci) depend on having a clock
driver to obtain the clock frequency.

Setting up the clock drivers properly is a bit tricky on U8500,
so for now add a simple fixed-clock for the eMMC that allows obtaining
the clock frequency. This should be replaced eventually if some board
actually requires enabling some of the clocks.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
diff --git a/arch/arm/dts/ste-dbx5x0-u-boot.dtsi b/arch/arm/dts/ste-dbx5x0-u-boot.dtsi
index 4a99ee5..e350175 100644
--- a/arch/arm/dts/ste-dbx5x0-u-boot.dtsi
+++ b/arch/arm/dts/ste-dbx5x0-u-boot.dtsi
@@ -4,8 +4,14 @@
 #include "ste-dbx5x0.dtsi"
 
 / {
+	/* FIXME: Remove this when clk driver is implemented */
+	sdmmcclk: sdmmcclk {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <100000000>;
+	};
+
 	soc {
-		/* FIXME: Remove this when clk driver is implemented */
 		mtu@a03c6000 {
 			clock-frequency = <133000000>;
 		};
@@ -18,6 +24,9 @@
 		uart@80007000 {
 			clock = <38400000>;
 		};
+		mmc@80005000 {
+			clocks = <&sdmmcclk>;
+		};
 	};
 
 	reboot {