renesas: Fix RPC-IF compatible values

The compatible values used for device nodes representing Renesas Reduced
Pin Count Interfaces were based on preliminary versions of the Device
Tree Bindings.

Correct them in both DTSi files and drivers, to match the final DT
Bindings.

Note that there are no DT bindings for RPC-IF on RZ/A1 yet, hence the
most logical SoC-specific value is used, without specifying a
family-specific value.

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