clocksource: sh_cmt: Add DT support

Document DT bindings and parse them in the CMT driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Simon Horman <horms+renesas@verge.net.au>

Documentation/devicetree/bindings/timer/renesas,cmt.txt

@@ -0,0 +1,47 @@
+* Renesas R-Car Compare Match Timer (CMT)
+
+The CMT is a multi-channel 16/32/48-bit timer/counter with configurable clock
+inputs and programmable compare match.
+
+Channels share hardware resources but their counter and compare match value
+are independent. A particular CMT instance can implement only a subset of the
+channels supported by the CMT model. Channel indices represent the hardware
+position of the channel in the CMT and don't match the channel numbers in the
+datasheets.
+
+Required Properties:
+
+  - compatible: must contain one of the following.
+    - "renesas,cmt-32" for the 32-bit CMT
+		(CMT0 on sh7372, sh73a0 and r8a7740)
+    - "renesas,cmt-32-fast" for the 32-bit CMT with fast clock support
+		(CMT[234] on sh7372, sh73a0 and r8a7740)
+    - "renesas,cmt-48" for the 48-bit CMT
+		(CMT1 on sh7372, sh73a0 and r8a7740)
+    - "renesas,cmt-48-gen2" for the second generation 48-bit CMT
+		(CMT[01] on r8a73a4, r8a7790 and r8a7791)
+
+  - reg: base address and length of the registers block for the timer module.
+  - interrupts: interrupt-specifier for the timer, one per channel.
+  - clocks: a list of phandle + clock-specifier pairs, one for each entry
+    in clock-names.
+  - clock-names: must contain "fck" for the functional clock.
+
+  - renesas,channels-mask: bitmask of the available channels.
+
+
+Example: R8A7790 (R-Car H2) CMT0 node
+
+	CMT0 on R8A7790 implements hardware channels 5 and 6 only and names
+	them channels 0 and 1 in the documentation.
+
+	cmt0: timer@ffca0000 {
+		compatible = "renesas,cmt-48-gen2";
+		reg = <0 0xffca0000 0 0x1004>;
+		interrupts = <0 142 IRQ_TYPE_LEVEL_HIGH>,
+			     <0 142 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&mstp1_clks R8A7790_CLK_CMT0>;
+		clock-names = "fck";
+
+		renesas,channels-mask = <0x60>;
+	};