KVM: arm64: nv: Add FGT registers

Add the 5 registers covering FEAT_FGT. The AMU-related registers
are currently left out as we don't have a plan for them. Yet.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Miguel Luis <miguel.luis@oracle.com>
Reviewed-by: Jing Zhang <jingzhangos@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230815183903.2735724-13-maz@kernel.org