Impact: add better first percpu allocation for NUMA

On NUMA, embedding allocator can't be used as different units can't be
made to fall in the correct NUMA nodes.  To use large page mapping,
each unit needs to be remapped.  However, percpu areas are usually
much smaller than large page size and unused space hurts a lot as the
number of cpus grow.  This allocator remaps large pages for each chunk
but gives back unused part to the bootmem allocator making the large
pages mapped twice.

This adds slightly to the TLB pressure but is much better than using
4k mappings while still being NUMA-friendly.

Ingo suggested that this would be the correct approach for NUMA.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>