radix tree test suite: add allocation counts and size to kmem_cache

radix tree test suite: add allocation counts and size to kmem_cache

Add functions to get the number of allocations, and total allocations from
a kmem_cache.  Also add a function to get the allocated size and a way to
zero the total allocations.

Link: https://lkml.kernel.org/r/20220504010716.661115-6-Liam.Howlett@oracle.com
Link: https://lkml.kernel.org/r/20220621204632.3370049-5-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>