vxge: serialize access to steering control register

It is possible for multiple callers to access the firmware interface for
the same vpath simultaneously, resulting in uncertain output.  Add locks
to serialize access.  Also, make functions only accessed locally static,
thus requiring some movement of code blocks.

Signed-off-by: Jon Mason <jon.mason@exar.com>
Signed-off-by: Ram Vepa <ram.vepa@exar.com>
Signed-off-by: David S. Miller <davem@davemloft.net>