replace d->nr_pirqs sized arrays with radix tree

replace d->nr_pirqs sized arrays with radix tree

With this it is questionable whether retaining struct domain's
nr_pirqs is actually necessary - the value now only serves for bounds
checking, and this boundary could easily be nr_irqs.

Note that ia64, the build of which is broken currently anyway, is only
being partially fixed up.

v2: adjustments for split setup/teardown of translation data

v3: re-sync with radix tree implementation changes

Signed-off-by: Jan Beulich <jbeulich@novell.com>