arm64: zynqmp: Fix GIC compatible property

dtbs_check is showing warning around GIC compatible property as
interrupt-controller@f9010000: compatible: ['arm,gic-400', 'arm,cortex-a15-gic']
is not valid under any of the given schemas

Similar change has been done also by commit 5400cdc1
("ARM: dts: sunxi: Fix GIC compatible")

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/a50412fbb520954e4602f274f19a7ffbd1154ead.1582621224.git.michal.simek@xilinx.com