KVM: arm64: vgic-v3: Restrict SEIS workaround to known broken systems

Contrary to what df652bcf ("KVM: arm64: vgic-v3: Work around GICv3
locally generated SErrors") was asserting, there is at least one other
system out there (Cavium ThunderX2) implementing SEIS, and not in
an obviously broken way.

So instead of imposing the M1 workaround on an innocent bystander,
let's limit it to the two known broken Apple implementations.

Fixes: df652bcf ("KVM: arm64: vgic-v3: Work around GICv3 locally generated SErrors")
Reported-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220122103912.795026-1-maz@kernel.org