sh-pfc: Remove unused macro and enum entries

The SH_PFC_MARK_INVALID macro and the PINMUX_FLAG_TYPE, GPIO_CFG_REQ and
GPIO_CFG_FREE enum entries are used, remove them.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Yusuke Goda <yusuke.goda.sx@renesas.com>