net/mlx5: Expose cable_length field in PFCC register

Introduce new "cable_length" field in PFCC register and related fields
to enhance rx buffer configuration management:
1. cable_length: Shifts cable length handling to fw by storing a
   manually entered length from user in PFCC.cable_length
2. lane_rate_oper: In a case where PFCC.cable_length is not supported,
   helps compute a default cable length

Signed-off-by: Oren Sidi <osidi@nvidia.com>
Reviewed-by: Alex Lazar <alazar@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1752734895-257735-4-git-send-email-tariqt@nvidia.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>