KVM: arm64: Add Fine-Grained UNDEF tracking information

KVM: arm64: Add Fine-Grained UNDEF tracking information

In order to efficiently handle system register access being disabled,
and this resulting in an UNDEF exception being injected, we introduce
the (slightly dubious) concept of Fine-Grained UNDEF, modeled after
the architectural Fine-Grained Traps.

For each FGT group, we keep a 64 bit word that has the exact same
bit assignment as the corresponding FGT register, where a 1 indicates
that trapping this register should result in an UNDEF exception being
reinjected.

So far, nothing populates this information, nor sets the corresponding
trap bits.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240214131827.2856277-18-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>