dt-bindings: timer: renesas,tmu: Document input capture interrupt

Some Timer Unit (TMU) instances with 3 channels support a fourth
interrupt: an input capture interrupt for the third channel.

While at it, document the meaning of the four interrupts, and add
"interrupt-names" for clarity.

Update the example to match reality.

Inspired by a patch by Yoshinori Sato for SH.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/8cb38b5236213a467c6c0073f97ccc4bfd5a39ff.1706717378.git.geert+renesas@glider.be

Author: geertu

Documentation/devicetree/bindings/timer/renesas,tmu.yaml

@@ -46,7 +46,19 @@ properties:
 
   interrupts:
     minItems: 2
-    maxItems: 3
+    items:
+      - description: Underflow interrupt, channel 0
+      - description: Underflow interrupt, channel 1
+      - description: Underflow interrupt, channel 2
+      - description: Input capture interrupt, channel 2
+
+  interrupt-names:
+    minItems: 2
+    items:
+      - const: tuni0
+      - const: tuni1
+      - const: tuni2
+      - const: ticpi2
 
   clocks:
     maxItems: 1
@@ -100,7 +112,9 @@ examples:
             reg = <0xffd80000 0x30>;
             interrupts = <GIC_SPI 32 IRQ_TYPE_LEVEL_HIGH>,
                          <GIC_SPI 33 IRQ_TYPE_LEVEL_HIGH>,
-                         <GIC_SPI 34 IRQ_TYPE_LEVEL_HIGH>;
+                         <GIC_SPI 34 IRQ_TYPE_LEVEL_HIGH>,
+                         <GIC_SPI 35 IRQ_TYPE_LEVEL_HIGH>;
+            interrupt-names = "tuni0", "tuni1", "tuni2", "ticpi2";
             clocks = <&mstp0_clks R8A7779_CLK_TMU0>;
             clock-names = "fck";
             power-domains = <&sysc R8A7779_PD_ALWAYS_ON>;