sh-pfc: r8a7779: Don't use GPIO enum entries

Refactor the GPIO macro magic to use GPIO numbers directly instead of
the GPIO_GP_x_y enum entries. This will allow removing the GPIO enum
entries from the mach/r8a7779.h header.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>