pinctrl: renesas: Add PORT_GP_CFG_19 macros

Add PORT_GP_CFG_19() and PORT_GP_19() helper macros, to be used by the
r8a779f0 subdriver.

Based on a larger patch in the BSP by LUU HOAI.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/f7fc711d065f78911bac1b616880ba3dbc858158.1645457792.git.geert+renesas@glider.be