media: atomisp: hmm_bo: Drop PFN code path from alloc_user_pages()

alloc_user_pages() is only ever called on qbuf for USERPTR buffers which
always hits the get_user_pages_fast() path, so the pin_user_pages() path
can be removed.

Getting the vma then also is no longer necessary since that is only
done to determine which path to use.

And this also removes the only users of the mem_type struct hmm_bo member,
so remove that as well.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>