KVM: arm64: selftests: Filter out DEMUX registers

DEMUX register presence depends on the host's hardware (the
CLIDR_EL1 register to be precise). This means there's no set
of them that we can bless and that it's possible to encounter
new ones when running on different hardware (which would
generate "Consider adding them ..." messages, but we'll never
want to add them.)

Remove the ones we have in the blessed list and filter them
out of the new list, but also provide a new command line switch
to list them if one so desires.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201126134641.35231-3-drjones@redhat.com