irqchip/gic-v3: Probe device ID space before quirks handling

Before adding another SoC whose device ID space deviates from the
value presented in the GIC ID registers, let's slightly refactor
the code so that the ID registers are probed before that quirks
handling executes. This allows us to move the device ID override
into the quirk handler itself.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>