RDMA/bnxt_re: Support doorbell extensions

RDMA/bnxt_re: Support doorbell extensions

Some applications may need multiple doorbells to support parallel
processing of threads that each operate on a group of resources.

The following uapi methods have been implemented in this patch.

- BNXT_RE_METHOD_DBR_ALLOC:
  This will allow the appliation to create extra doorbell regions
  and use the associated doorbell page index in CREATE_QP and
  use the associated DB address while ringing the doorbell.

- BNXT_RE_METHOD_DBR_FREE:
  Free the allocated doorbell region.

- BNXT_RE_METHOD_GET_DEFAULT_DBR:
  Return the default doorbell page index and doorbell page address
  associated with the ucontext.

Link: https://patch.msgid.link/r/20260302110036.36387-4-sriharsha.basavapatna@broadcom.com
Co-developed-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Signed-off-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Reviewed-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>