IB/mlx5: Move and decouple user vendor structures

This patch decouples and moves vendors specific structures to
common UAPI folder which will be visible to all consumers.

These structures are used by user-space library driver
(libmlx5) and currently manually copied to that library.

This move will allow cross-compile against these files and
simplify introduction of vendor specific data.

Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>