RDMA/bnxt_re: Avoid repeated requests to allocate WC pages

RDMA/bnxt_re: Avoid repeated requests to allocate WC pages

Applications can request multiple WC pages for the same ucontext.
As of now, only 1 WC page per ucontext is supported. Add a lock to
avoid concurrent access and a check to fail repeated requests.
Also, if the mmap entry insert fails for the WC, free the Doorbell
page index mapped for the WC page.

Fixes: eee6268421a2 ("RDMA/bnxt_re: Move the UAPI methods to a dedicated file")
Fixes: 360da60d6c6e ("RDMA/bnxt_re: Enable low latency push")
Link: https://patch.msgid.link/r/20260615224751.232802-12-selvin.xavier@broadcom.com
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>