dt-bindings: pwm: renesas: tpu: Fix "compatible" prop description

The "compatible" property description contradicts even the example given:
it only says that there must be a single value while the example has the
fallback value too -- which makes much more sense. Moreover, the generic
property value is misdocumented as being R-Car (and RZ/G1) specific...

Fixes: 382457e5 ("pwm: renesas-tpu: Add DT support")
Fixes: 3ba111a0 ("dt-bindings: pwm: renesas-tpu: Document r8a774[35] support")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/renesas,tpu-pwm.txt

@@ -2,13 +2,14 @@
 
 Required Properties:
 
-  - compatible: should be one of the following.
+  - compatible: must contain one or more of the following:
     - "renesas,tpu-r8a73a4": for R8A73A4 (R-Mobile APE6) compatible PWM controller.
     - "renesas,tpu-r8a7740": for R8A7740 (R-Mobile A1) compatible PWM controller.
     - "renesas,tpu-r8a7743": for R8A7743 (RZ/G1M) compatible PWM controller.
     - "renesas,tpu-r8a7745": for R8A7745 (RZ/G1E) compatible PWM controller.
     - "renesas,tpu-r8a7790": for R8A7790 (R-Car H2) compatible PWM controller.
-    - "renesas,tpu": for generic R-Car and RZ/G1 TPU PWM controller.
+    - "renesas,tpu": for the generic TPU PWM controller; this is a fallback for
+		     the entries listed above.
 
   - reg: Base address and length of each memory resource used by the PWM
     controller hardware module.