watchdog: sp805_wdt: use correct compatible string

According to the linux device tree specification the compatible string
is:
  compatible = "arm,sp805", "arm,primecell";

Fix all users in u-boot.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/arch/arm/dts/fsl-ls1028a.dtsi b/arch/arm/dts/fsl-ls1028a.dtsi
index e5b5a0d..cbdddcc 100644
--- a/arch/arm/dts/fsl-ls1028a.dtsi
+++ b/arch/arm/dts/fsl-ls1028a.dtsi
@@ -382,7 +382,7 @@
 		};
 
 		cluster1_core0_watchdog: wdt@c000000 {
-			compatible = "arm,sp805-wdt";
+			compatible = "arm,sp805", "arm,primecell";
 			reg = <0x0 0xc000000 0x0 0x1000>;
 		};