Isolate hardware abstraction (FDT) code to gic_of_init().
Rest of the logic goes to gic_init_bases() and expects well
defined data to initialize GIC properly. The same solution
is used for GICv2 driver.

This is needed for ACPI initialization later.
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NTomasz Nowicki <tomasz.nowicki@linaro.org>
Signed-off-by: NHanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>