ARM: dts: ast2600evb: Enable UART workaround

The UART has an issue on A0 that can be worked around by using the
Synopsis driver.
Tested-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>

arch/arm/boot/dts/aspeed-ast2600-evb.dts

@@ -147,3 +147,8 @@ flash@0 {
 		spi-max-frequency = <100000000>;
 	};
 };
+
+&uart5 {
+	// Workaround for A0
+	compatible = "snps,dw-apb-uart";
+};