IB/mthca: Move user vendor structures

This patch moves mthca vendor's specific structures to
common UAPI folder which will be visible to all consumers.

These structures are used by user-space library driver
(libmthca) 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>