RDMA/core: Add new IB rate for XDR (8x) support

RDMA/core: Add new IB rate for XDR (8x) support

Add the new rates as defined in the Infiniband spec for XDR and 8x
link width support.

Furthermore, modify the utility conversion methods accordingly.

Reference: IB Spec Release 1.8

Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Link: https://patch.msgid.link/20251120-speed-8-v1-1-e6a7efef8cb8@nvidia.com
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>