clocksource: sh_tmu: Document R-Mobile r8a7740 binding

Compared to the r8a7779, the r8a7740 lacks the input capture register,
which is not used by the driver (the current driver already handles the
r8a7740 in the non-DT case).
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

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

-* Renesas R-Car Timer Unit (TMU)
+* Renesas R-Mobile/R-Car Timer Unit (TMU)
 
 The TMU is a 32-bit timer/counter with configurable clock inputs and
 programmable compare match.
@@ -9,6 +9,7 @@ are independent. The TMU hardware supports up to three channels.
 Required Properties:
 
   - compatible: must contain one or more of the following:
+    - "renesas,tmu-r8a7740" for the r8a7740 TMU
     - "renesas,tmu-r8a7779" for the r8a7779 TMU
     - "renesas,tmu" for any TMU.
       This is a fallback for the above renesas,tmu-* entries