io_uring/rsrc: export io_check_coalesce_buffer

io_try_coalesce_buffer() is a useful helper collecting useful info about
a set of pages, I want to reuse it for analysing ring/etc. mappings. I
don't need the entire thing and only interested if it can be coalesced
into a single page, but that's better than duplicating the parsing.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/353b447953cd5d34c454a7d909bb6024c391d6e2.1732886067.git.asml.silence@gmail.com


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