RDMA/efa: Do not delay freeing of DMA pages

When destroying a DMA mmapped object, there is no need to artificially
delay the freeing of the pages to the mmap entry removal.  Since the vma
keeps a reference count on these pages, free_pages_exact can be called on
the destroy verb as it won't really free the pages until the reference
count is cleared (in case the user hasn't called munmap yet).

Remove the special handling of DMA pages and call free_pages_exact on
destroy_qp/cq. The mmap entry removal is moved to the beginning of the
destroy flows, so the driver can safely free the pages.

Link: https://lore.kernel.org/r/20200225114010.21790-4-galpress@amazon.com


Reviewed-by: Firas JahJah <firasj@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>