clk: renesas: r8a774a1: Add RPC clocks

Describe the RPCSRC internal clock and the RPC[D2] clocks derived from it,
as well as the RPC-IF module clock, in the RZ/G2M (R8A774A1) CPG/MSSR
driver.

Inspired by commit 94e3935b ("clk: renesas: r8a77980: Add RPC clocks").

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20201016121709.8447-3-prabhakar.mahadev-lad.rj@bp.renesas.com


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