refactor(plat/rockchip/rk3399/drivers/gpio): reduce code duplication

Refactor the GPIO code to use a small lookup table instead of redundant or
repetitive code.

Signed-off-by: Jona Stubbe <tf-a@jona-stubbe.de>
Change-Id: Icf60385095efc1f506e4215d497b60f90e16edfd
Signed-off-by: Jimmy Brisson <jimmy.brisson@arm.com>
4 files changed