In the beginning, life was simple. The GIC driver mostly cared about
PPIs, SPIs and LPIs, all with nicely layed out ranges.

We're about to change all that, with new ranges such as EPPI and ESPI
interleaved in the middle of the no-irq-land between the "special IDs"
and the LPI range. Boo.

In order to make our life less hellish, let's introduce a set of primitives
that will allow ranges to be identified easily and offsets to be remapped.

So far, there is no functionnal change.
Signed-off-by: Marc Zyngier <maz@kernel.org>