ARM: dts: aspeed: rainier: Enable earlycon

Rainier was missed when enabling all of the other machines in
commit 239566b032f3 ("ARM: dts: aspeed: Set earlycon boot argument").

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/arch/arm/boot/dts/aspeed-bmc-ibm-rainier.dts b/arch/arm/boot/dts/aspeed-bmc-ibm-rainier.dts
index f38c44b..866f32c 100644
--- a/arch/arm/boot/dts/aspeed-bmc-ibm-rainier.dts
+++ b/arch/arm/boot/dts/aspeed-bmc-ibm-rainier.dts
@@ -82,7 +82,7 @@ aliases {
 
 	chosen {
 		stdout-path = &uart5;
-		bootargs = "console=ttyS4,115200n8";
+		bootargs = "console=ttyS4,115200n8 earlycon";
 	};
 
 	memory@80000000 {