dt-bindings: pwm: renesas-tpu: Document r8a7744 support

Document r8a7744 specific compatible strings. No driver change is
needed as the fallback compatible string "renesas,tpu" activates the
right code in the driver.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

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

@@ -6,6 +6,7 @@ Required Properties:
     - "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-r8a7744": for R8A7744 (RZ/G1N) 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-r8a77970": for R8A77970 (R-Car V3M) compatible PWM