clk: renesas: rzg2l: Add CPG_PL1_DDIV macro

clk: renesas: rzg2l: Add CPG_PL1_DDIV macro

Core clock "I" is sourced from  CPG_PL1_DDIV which controls CPU
frequency. Define CPG_PL1_DDIV, so that we can register it as a
clock divider in later patch.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20211112081003.15453-2-biju.das.jz@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>