cpuallocator: add cache group based allocation.

Implement cache group based CPU allocation. When a request
makes this possible, try to satisfy it by allocating one or
more cache groups. Always prefer using fully idle cache groups
first, fragmenting idle cache groups by partial allocation
second, and only resort to using fragmented groups when the
allocation cannot be satisfied in any other way. When doing
partial allocations, do it in a hyperthreading aware fashion,
taking full physical cores whenever possible.

Note:
  This allocation algorithm is a modified version of the
  cluster based allocator. We might want to try and combine
  them into a single group based allocator in the future.

Signed-off-by: Krisztian Litkey <[email protected]>