Docs/mm/damon/design: document DAMON actions when TRANSPARENT_HUGEPAGE is off

Docs/mm/damon/design: document DAMON actions when TRANSPARENT_HUGEPAGE is off

MADV_HUGEPAGE and MADV_NOHUGEPAGE are guarded and they are not available
when compiling the kernel without TRANSPARENT_HUGEPAGE option.  The DAMON
behaviour is to silently fail [1] in when DAMOS_HUGEPAGE or
DAMOS_NOHUGEPAGE are used, but TRANSPARENT_HUGEPAGE is disabled.  Update
the DAMON documentation to reflect this behaviour.

Link: https://lkml.kernel.org/r/20260318035349.88715-1-sj@kernel.org
Link: https://lore.kernel.org/66131775-180b-4b9f-b7ce-61a3e077b6e6@huawei-partners.com/
Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>