mlx5_core: Import PDDR register definitions

mlx5_core: Import PDDR register definitions

PDDR (Port Diagnostics Database Register) is used to read the physical
layer debug database, which contains helpful troubleshooting information
regarding the state of the link.

PDDR register can only be queried when PCAM register reports it as
supported in its register mask. A new helper macro was added to
the MLX5_CAP_* infrastructure in order to access this mask.

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