sh-pfc: Don't duplicate argument to PINMUX_GPIO macro

The PINMUX_GPIO macro takes a port name and a data mark, respectively of
the form GPIO_name and name_DATA. Modify the macro to take the name as a
single argument and derive the port name and data mark from it.

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