irqdomain: Implement and expose API to clear IRQ mapping for radix tree

The irq_domain_remove() API expects all the irqs of the domain be cleared
before it is called, else it throws a warning. A framework creating a
radix tree to map all the irqs used by its clients cannot be sure if all
the clients cleared their irqs. Thus to avoid this warning, we can use
this API irq_dispose_all_tree_mappings() to ensure that all irqs
belonging to the domain are cleared before the domain is itself removed.

Change-Id: Ied1f20c990aba9d4760091d9ed3d48c3e4f3d5d9
Signed-off-by: Prakruthi Deepak Heragu <pheragu@codeaurora.org>