Convert the cpu source to do feature discovery and creation of feature
labels separately.
Move cpuidutils from source/internal to the source/cpu package. Change
the cpuid custom rule to utilize GetFeatures of the cpu source.
Also, add minimalist unit test.
This provides support for 32-bit ARM cpuid capabilities based on
the HWCAP flags, and enables the build of NFD on the 32-bit ARM
userland - notably, this also applies to ARM64 systems that are
running userspace in Aarch32 mode, which is where this problem
was first encountered.
Signed-off-by: Paul Mundt <paul.mundt@adaptant.io>
