ARM: dts: keystone: Add clock phandle to UART nodes

Now since the clock tree is added, update UART dt nodes with clock data
and remove the hard coded clock frequency.
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

arch/arm/boot/dts/keystone.dts

@@ -108,7 +108,7 @@ uart0: serial@02530c00 {
 			reg-shift = <2>;
 			reg-io-width = <4>;
 			reg = <0x02530c00 0x100>;
-			clock-frequency = <133120000>;
+			clocks	= <&clkuart0>;
 			interrupts = <GIC_SPI 277 IRQ_TYPE_EDGE_RISING>;
 		};
 
@@ -118,7 +118,7 @@ uart1:	serial@02531000 {
 			reg-shift = <2>;
 			reg-io-width = <4>;
 			reg = <0x02531000 0x100>;
-			clock-frequency = <133120000>;
+			clocks	= <&clkuart1>;
 			interrupts = <GIC_SPI 280 IRQ_TYPE_EDGE_RISING>;
 		};