Replace the mmap handling function with common code in IB core. Create
rdma_user_mmap_entry for each mmap resource and add to the ib_core mmap
list. Add mmap_free verb support. Also, use rdma_user_mmap_io while
mapping Doorbell pages.

Link: https://lore.kernel.org/r/1686679943-17117-2-git-send-email-selvin.xavier@broadcom.comSigned-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>