clk: renesas: Pass sub struct of cpg_mssr_priv to cpg_clk_register

clk: renesas: Pass sub struct of cpg_mssr_priv to cpg_clk_register

In a subsequent patch, the registration callback will need more parameters
from cpg_mssr_priv (like another base address with clock controllers
with double register block, and also, notifiers and rmw_lock).
Instead of adding more parameters, move the needed parameters to a public
sub-struct.
Instead moving clks to this structure, which would have implied to add
an allocation (and cleanup) for it, keep the way the allocation is done
and just have a copy of the pointer in the public structure.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Thierry Bultel <thierry.bultel.yh@bp.renesas.com>
Link: https://lore.kernel.org/20250515141828.43444-5-thierry.bultel.yh@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>