arm64: Document workaround for Cortex-A72 erratum #853709

We already have a workaround for Cortex-A57 erratum #852523,
but Cortex-A72 r0p0 to r0p2 do suffer from the same issue
(known as erratum #853709).

Let's document the fact that we already handle this.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

arch/arm64/kvm/hyp/switch.c

@@ -256,7 +256,7 @@ static int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
 
 	/*
 	 * We must restore the 32-bit state before the sysregs, thanks
-	 * to Cortex-A57 erratum #852523.
+	 * to erratum #852523 (Cortex-A57) or #853709 (Cortex-A72).
 	 */
 	__sysreg32_restore_state(vcpu);
 	__sysreg_restore_guest_state(guest_ctxt);