io_uring/memmap: flag regions with user pages

In preparation to kernel allocated regions add a flag telling if
the region contains user pinned pages or not.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0dc91564642654405bab080b7ec911cb4a43ec6e.1732886067.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>