devicetree: bindings: Remove sh7372 CMT binding

Remove the sh7372 CMT compat string to reduce maintenance burden.

It should be fine to break DT compatibility because:
1) The sh7372 SoC support has been removed from upstream
2) The sh7372 CMT DT binding was never part of upstream DTS
3) The CMT driver never matches on the sh7372 binding

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>