The debug architecture is mandatory in ARMv8, so KVM should not allow
userspace to configure a vCPU with less than that. Of course, this isn't
handled elegantly by the generic ID register plumbing, as the respective
ID register fields have a nonzero starting value.

Add an explicit check for debug versions less than v8 of the
architecture.
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231003230408.3405722-5-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>