vxge: independent interrupt moderation

Configure the workload clock register and TIM register for independent
interrupt moderation based on the individual vpath utilization instead
of common link utilization.  This greatly improves latency.

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>