powerpc: dts: p2020: Add gpio-controller@fc00 node via pq3-gpio-0.dtsi

Import pq3-gpio-0.dtsi device tree include file from upstream Linux kernel
for P2020. This allows U-Boot to use P2020 device tree files from upstream
Linux kernel which reference gpio-controller@fc00 device.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>