Add the RPC pins/groups/functions to the R8A77970 PFC driver.
They can be used if an Octal-SPI flash or HyperFlash is connected.

Based on the patch by Dmitry Shifrin <dmitry.shifrin@cogentembedded.com>.
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Link: https://lore.kernel.org/r/3982785f-4fca-96f9-2b6a-a0d1828cb0ad@cogentembedded.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>