mm: huge_memory: refactor defrag_show() to use defrag_flags[]

mm: huge_memory: refactor defrag_show() to use defrag_flags[]

Replace the hardcoded if/else chain of test_bit() calls and string
literals in defrag_show() with a loop over defrag_flags[] and
defrag_mode_strings[] arrays introduced in the previous commit.

This makes defrag_show() consistent with defrag_store() and eliminates the
duplicated mode name strings.

Link: https://lore.kernel.org/20260408-thp_defrag-v2-2-bc544c1bde4e@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Tested-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>