pinctrl: renesas: Add PORT_GP_CFG_7 macros

Add PORT_GP_CFG_7() and PORT_GP_7() helper macros, to be used by the
r8a7791 subdriver.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20210303132619.3938128-5-geert+renesas@glider.be