GPIO / ACPI: export acpi_gpiochip_request(free)_interrupts for module use

acpi_gpiochip_request(free)_interrupts can be used for modules,
so export them. This also fixs a compile error when xgene-sb
configured as kernel module.

Fixes: 733cf014 "gpio: xgene: add ACPI support for APM X-Gene GPIO standby driver"
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>