Way to allocate a specific u32 in the IdAllocator

[ramyak-mehra]

there is currently no way of allocating a particular id in the IdAllocator.

[andreeaflorescu]

This functionality is need to be able to allocate IRQs for legacy devices on x86_64. Right now just adding allocate_exact_id is not really straightforward because of the design of the IdAllocator.