Remove 'cpuid', 'pstate' and 'rdt' feature sources and move their
functionality under the 'cpu' source. The goal is to have a more
systematic organization of feature sources and labels. After this change
we now basically have one source per type of hw, one for kernel and one
for userspace sw.
Related feature labels are changed, correspondingly, new labels being:
feature.node.k8s.io/cpu-cpuid.<cpuid flag>
feature.node.k8s.io/cpu-pstate.turbo
feature.node.k8s.io/cpu-rdt.<rdt feature>
Move most of the code under cmd/nfd-master and cmd/nfd-worker into new
packages pkg/nfd-master and pk/nfd-worker, respectively. Makes extending
unit tests to "main" functions easier.
