KVM: arm64: Make ID_AA64PFR0_EL1.RAS writable

Make ID_AA64PFR0_EL1.RAS writable so that we can restore a VM from
a system without RAS to a RAS-equipped machine (or disable RAS
in the guest).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/r/20250817202158.395078-5-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: Marc Zyngier

arch/arm64/kvm/sys_regs.c

@@ -2939,7 +2939,6 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 		    ~(ID_AA64PFR0_EL1_AMU |
 		      ID_AA64PFR0_EL1_MPAM |
 		      ID_AA64PFR0_EL1_SVE |
-		      ID_AA64PFR0_EL1_RAS |
 		      ID_AA64PFR0_EL1_AdvSIMD |
 		      ID_AA64PFR0_EL1_FP)),
 	ID_FILTERED(ID_AA64PFR1_EL1, id_aa64pfr1_el1,