dt-bindings: timer: renesas: tmu: document R8A779{7|8}0 bindings

Document the R-Car V3{M|H} (R8A779{7|8}0) SoC in the Renesas TMU bindings;
the TMU hardware in those is the Renesas standard 3-channel timer unit.
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

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

@@ -12,6 +12,8 @@ Required Properties:
     - "renesas,tmu-r8a7740" for the r8a7740 TMU
     - "renesas,tmu-r8a7778" for the r8a7778 TMU
     - "renesas,tmu-r8a7779" for the r8a7779 TMU
+    - "renesas,tmu-r8a77970" for the r8a77970 TMU
+    - "renesas,tmu-r8a77980" for the r8a77980 TMU
     - "renesas,tmu" for any TMU.
       This is a fallback for the above renesas,tmu-* entries