irqchip/gic: Rework gic_configure_irq to take the full ICFGR base

gic_configure_irq is currently passed the (re)distributor address,
to which it applies an a fixed offset to get to the configuration
registers. This offset is constant across all GICs, or rather it was
until to v3.1...

An easy way out is for the individual drivers to pass the base
address of the configuration register for the considered interrupt.
At the same time, move part of the error handling back to the
individual drivers, as things are about to change on that front.

Signed-off-by: Marc Zyngier <maz@kernel.org>