mm/slab: make caches with sheaves mergeable

mm/slab: make caches with sheaves mergeable

Before enabling sheaves for all caches (with automatically determined
capacity), their enablement should no longer prevent merging of caches.
Limit this merge prevention only to caches that were created with a
specific sheaf capacity, by adding the SLAB_NO_MERGE flag to them.

Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>