pinctrl: sh-pfc: Add R8A7792 PFC support

Add the PFC support for the R8A7792 SoC including pin groups for some
on-chip devices such as SCIF, INTC, and LBSC...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
[geert: s/LSBC/LBSC/]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>