mm/show_mem.c: report alloc tags in human readable units

We already do this when reporting slab info - more consistent and more
readable.

Link: https://lkml.kernel.org/r/20240906005337.1220091-1-kent.overstreet@linux.dev


Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>