pinctrl: sh-pfc: Move PIN_NONE to shared header file

Several drivers have identical definitions for PIN_NONE.
Provide a definition with a SH_PFC_ prefix for general use in sh_pfc.h,
and convert all drivers over to use it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>