IB/mlx5: Avoid calling query device for reading pkey table length

Pkey table length for all the ports of the device is the same.  Currently
get_ports_cap() reads and stores it for each port by querying the device
which reads more than just pkey table length.

For representor device ports which can be in range of hundreds, it queries
is for each such port and end up returning same value for all the ports.

When in representor mode, modify QP accesses pkey port caps for a port
index that can be outside of the port_caps table.

Hence, simplify the logic to query the max pkey table length only once
during device initialization sequence.

Link: https://lore.kernel.org/r/20210203130133.4057329-3-leon@kernel.org


Signed-off-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>