gpio: do not include <asm/arch/gpio.h> for Cortina CAxxxx SoCs

The Cortina CAxxxx GPIO driver maintains DM_GPIO support
across different CPU ISA in the CAxxxx Soc Family; Not just ARM.
Therefore, it is not desirable to split out and maintain separete
gpio header file for each CPU architecture.

Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Jason Li <jason.li@cortina-access.com>
Signed-off-by: Alex Nemirovsky <alex.nemirovsky@cortina-access.com>