clk: renesas: r8a77995: Add RPC clocks

Describe the various clocks used by the SPI Multi I/O Bus Controller
(RPC-IF) on the R-Car D3 SoC: RPCSRC internal clock, RPC{,D2} clocks
derived from it, and RPC-IF module clock.

The RPCSRC clock divider on R-Car D3 is very similar to the one on R-Car
E3, but uses a different pre-divider for the PLL0 parent.  Add a new
macro to describe it, reusing the existing clock type for R-Car E3.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/3fd1e886b7737cd0e199603bae81d01be9dcf3aa.1648546700.git.geert+renesas@glider.be