Update the alloc_page uapi functionality for handling the
mapping of doorbell pacing shared page and bar address.

Link: https://lore.kernel.org/r/1689742977-9128-6-git-send-email-selvin.xavier@broadcom.comSigned-off-by: Chandramohan Akula <chandramohan.akula@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>