clk: renesas: rzg2l: Make use of CLK_MON registers optional

The RZ/V2M SoC doesn't use CLK_MON registers, so make them optional.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20220503115557.53370-9-phil.edworthy@renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>