clocksource: Add Allwinner SoCs HS timers driver

Most of the Allwinner SoCs (at this time, all but the A10) also have a
High Speed timers that are not using the 24MHz oscillator as a source
but rather the AHB clock running much faster.

The IP is slightly different between the A10s/A13 and the one used in
the A20/A31, since the latter have 4 timers available, while the former
have only 2 of them.

[dlezcano] : Fixed conflict with b788beda "Order Kconfig options
		alphabetically"

Signed-off-by: Maxime Ripard <[email protected]>
Tested-by: Emilio López <[email protected]>
Signed-off-by: Daniel Lezcano <[email protected]>

Documentation/devicetree/bindings/timer/allwinner,sun5i-a13-hstimer.txt

@@ -0,0 +1,22 @@
+Allwinner SoCs High Speed Timer Controller
+
+Required properties:
+
+- compatible :	should be "allwinner,sun5i-a13-hstimer" or
+		"allwinner,sun7i-a20-hstimer"
+- reg : Specifies base physical address and size of the registers.
+- interrupts :	The interrupts of these timers (2 for the sun5i IP, 4 for the sun7i
+		one)
+- clocks: phandle to the source clock (usually the AHB clock)
+
+Example:
+
+timer@01c60000 {
+	compatible = "allwinner,sun7i-a20-hstimer";
+	reg = <0x01c60000 0x1000>;
+	interrupts = <0 51 1>,
+		     <0 52 1>,
+		     <0 53 1>,
+		     <0 54 1>;
+	clocks = <&ahb1_gates 19>;
+};