gpio: cortina_gpio: add DM_GPIO driver for CAxxxx SoCs

DM_GPIO based GPIO controller driver for CAxxxx SoCs.
This driver support multiple CPU architectures and
Cortina Access SoC platforms.

Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Signed-off-by: Jason Li <jason.li@cortina-access.com>
Signed-off-by: Alex Nemirovsky <alex.nemirovsky@cortina-access.com>