clk: renesas: rzg2l: Add support for enabling PLLs

clk: renesas: rzg2l: Add support for enabling PLLs

Add support for enabling PLL clocks in the RZ/G3L CPG driver to turn off
some PLLs, if they are not in use (e.g. PLL6, PLL7).

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

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20260326110648.29389-3-biju.das.jz@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>