powerpc/fsl: update compatiable on fsl 16550 uart nodes

The Freescale serial port's are pretty much a 16550, however there are
some FSL specific bugs and features.  Add a "fsl,ns16550" compatiable
string to allow code to handle those FSL specific issues.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/boot/dts/mpc8313erdb.dts

@@ -261,7 +261,7 @@
 		serial0: serial@4500 {
 			cell-index = <0>;
 			device_type = "serial";
-			compatible = "ns16550";
+			compatible = "fsl,ns16550", "ns16550";
 			reg = <0x4500 0x100>;
 			clock-frequency = <0>;
 			interrupts = <9 0x8>;
@@ -271,7 +271,7 @@
 		serial1: serial@4600 {
 			cell-index = <1>;
 			device_type = "serial";
-			compatible = "ns16550";
+			compatible = "fsl,ns16550", "ns16550";
 			reg = <0x4600 0x100>;
 			clock-frequency = <0>;
 			interrupts = <10 0x8>;