buffers: support disabling allocation per numa domain

buffers: support disabling allocation per numa domain

Currently, the per-numa buffer allocation doesn't support skipping the
allocation altogether for a particular NUMA domain - if it's set to
zero, it instead uses the default allocation.

Therefore, this changes the behavior so that the default is only used
if no per-numa allocation is specified, and an allocation of zero
is honored by not allocating a buffer at all.

Type: improvement
Change-Id: Ie9133b179a88eb884aa3da921e65292daea0df2d
Signed-off-by: Lukas Stockner <[email protected]>