ARM: dts: keystone: drop address and size cells from GIC node

This is likely a copy-and-paste error from the
ARM GIC documentation, that has already been fixed.

address-cells should have been set to 0, as with the size
cells. As having those properties set to 0 is the
same thing as not specifying them, drop them completely.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>