io_uring/memmap: flag vmap'ed regions

Add internal flags for struct io_mapped_region. The first flag we need
is IO_REGION_F_VMAPPED, that indicates that the pointer has to be
unmapped on region destruction. For now all regions are vmap'ed, so it's
set unconditionally.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/5a3d8046a038da97c0f8a8c8f1733fa3fc689d31.1732886067.git.asml.silence@gmail.com


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