IB/mthca: Use PCI-X/PCI-Express read control interfaces

These driver changes incorporate the proposed PCI-X / PCI-Express read
byte count interface.  Reading and setting those values doesn't take
place "manually", instead wrapping functions are called to allow
quirks for some PCI bridges.

Signed-off by: Peter Oruba <peter.oruba@amd.com>
Based on work by Stephen Hemminger <shemminger@linux-foundation.org>
Cc: Roland Dreier <rolandd@cisco.com>
Cc: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Roland Dreier <rolandd@cisco.com>