cxgbe(4): sysctls to display the local and intr CPUs for the adapter.

The driver assumes the list can change (even though it does't right now)
and queries it every time the sysctl runs.

sysctl dev.<nexus>.<inst>.local_cpus
sysctl dev.<nexus>.<inst>.intr_cpus

sysctl dev.t6nex.0.local_cpus
sysctl dev.t6nex.0.intr_cpus

Sponsored by: Chelsio Communications