clk: renesas: rzv2h: Add support for enabling PLLs

clk: renesas: rzv2h: Add support for enabling PLLs

Some RZ/V2H(P) SoC variants do not have a GPU, resulting in PLLGPU being
disabled by default in TF-A. Add support for enabling PLL clocks in the
RZ/V2H(P) CPG driver to manage this.

Introduce `is_enabled` and `enable` callbacks to handle PLL state
transitions. With the `enable` callback, PLLGPU will be turned ON only
when the GPU node is enabled; otherwise, it will remain off. Define new
macros for PLL standby and monitor registers to facilitate this process.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250309211402.80886-4-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>