RDMA/bnxt_re: Enable low latency push

Introduce driver specific uapi functionalites. Added a alloc_page
functionality for user library to allocate specific pages. Currently added
support for allocating write combine pages for push functinality. This
interface shall be extended for other page allocations.

Allocate a WC page using the uapi hook for enabling the low latency push
in Gen P5 adapters for small packets. This is supported only for the user
space QPs.

Link: https://lore.kernel.org/r/1686679943-17117-8-git-send-email-selvin.xavier@broadcom.com
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>