dt-bindings: clock: renesas,rzg2l: Simplify header file references

The bindings already uses <dt-bindings/clock/r9a0*-cpg.h> to refer to
the header files with DT binding definitions for core clocks.
Use more wildcards to simplify more references to these files.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/f274ad16010798dd4a45d2dca5f870da8acbb470.1654696009.git.geert+renesas@glider.be