pinctrl: sh-pfc: r8a7796: Move CANFD pin groups and functions

CANFD is found also on the R8A774A1, therefore move CANFD pin
groups and functions to "common".

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Chris Paterson <chris.paterson2@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>