tools/testing/vma: clean up stubs in vma_internal.h

We do not need to references arguments just to avoid compiler warnings,
the warning in question does not arise here, so remove all of the
instances of '(void)xxx' introduced purely to avoid this warning.

As reported by WagYuli in the referenced mail, GCC 8.3 and before will
have issues compiling this file if parameter names are not provided, so
ensure these are always provided.

Finally, perform a trivial fix up of kmem_cache_alloc() which technically
has parameters in the incorrect order (as reported by Vlastimil Babka
off-list).

Link: https://lkml.kernel.org/r/20250826102824.22730-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reported-by: WangYuli <wangyuli@uniontech.com>
Closes: https://lore.kernel.org/linux-mm/EFCEBE7E301589DE+20250729084700.208767-1-wangyuli@uniontech.com/
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: WangYuli <wangyuli@uniontech.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Author: ljskernel