dt-bindings: timer: renesas,tmu: Add R-Mobile APE6 support

Document support for the Timer Unit (TMU) on the R-Mobile APE6 (R8A73A4)
Soc.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Reviewed-by: Niklas Söderlund <[e-mail]>
Reviewed-by: Wolfram Sang <[e-mail]>
Link: https://lore.kernel.org/r/17e3f[e-mail]
Signed-off-by: Daniel Lezcano <[e-mail]>

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

···
   compatible:
     items:
       - enum:
+          - renesas,tmu-r8a73a4  # R-Mobile APE6
           - renesas,tmu-r8a7740  # R-Mobile A1
           - renesas,tmu-r8a774a1 # RZ/G2M
           - renesas,tmu-r8a774b1 # RZ/G2N
···
       compatible:
         contains:
           enum:
+            - renesas,tmu-r8a73a4
             - renesas,tmu-r8a7740
             - renesas,tmu-r8a7778
             - renesas,tmu-r8a7779