xtensa: xtfpga: use common clock framework

With this change the board needs to set up single clock object, users of
this clock will get correct frequency automatically.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/boot/dts/xtfpga.dtsi

@@ -35,6 +35,13 @@ pic: pic {
 		interrupt-controller;
 	};
 
+	clocks {
+		osc: main-oscillator {
+			#clock-cells = <0>;
+			compatible = "fixed-clock";
+		};
+	};
+
 	serial0: serial@fd050020 {
 		device_type = "serial";
 		compatible = "ns16550a";
@@ -42,9 +49,7 @@ serial0: serial@fd050020 {
 		reg = <0xfd050020 0x20>;
 		reg-shift = <2>;
 		interrupts = <0 1>; /* external irq 0 */
-		/* Filled in by platform_setup from FPGA register
-		 * clock-frequency = <100000000>;
-		 */
+		clocks = <&osc>;
 	};
 
 	enet0: ethoc@fd030000 {

arch/xtensa/platforms/xtfpga/setup.c

@@ -135,11 +135,11 @@ static void __init update_local_mac(struct device_node *node)
 
 static int __init machine_setup(void)
 {
-	struct device_node *serial;
+	struct device_node *clock;
 	struct device_node *eth = NULL;
 
-	for_each_compatible_node(serial, NULL, "ns16550a")
-		update_clock_frequency(serial);
+	for_each_node_by_name(clock, "main-oscillator")
+		update_clock_frequency(clock);
 
 	if ((eth = of_find_compatible_node(eth, NULL, "opencores,ethoc")))
 		update_local_mac(eth);