irqchip/gic: Make quirks matching conditional on init return value

As it turns out, the IIDR is not sufficient to distinguish between GICv3
implementations when it comes to enabling quirks. So update the prototype
of the init() hook to return a bool, and interpret a 'false' return value
as no match, in which case the 'enabling workaround' log message should
not be printed.

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