dt-bindings: timer: renesas, cmt: Update CMT1 on sh73a0 and r8a7740

This patch reworks the DT binding documentation for the 6-channel
48-bit CMTs known as CMT1 on r8a7740 and sh73a0.

After the update the same style of DT binding as the rest of the upstream
SoCs will now also be used by r8a7740 and sh73a0. The DT binding "cmt-48"
is removed from the DT binding documentation, however software support for
this deprecated binding will still remain in the CMT driver for some time.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>