KVM: arm64: Advertise support for FEAT_DoubleFault2

KVM's external abort injection now respects the exception routing
wreckage due to FEAT_DoubleFault2. Advertise the feature.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250708172532.1699409-23-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: oupton

arch/arm64/kvm/sys_regs.c

@@ -1613,7 +1613,6 @@ static u64 __kvm_read_sanitised_id_reg(const struct kvm_vcpu *vcpu,
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_GCS);
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_THE);
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MTEX);
-		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_DF2);
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_PFAR);
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MPAM_frac);
 		break;
@@ -2884,7 +2883,6 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 		      ID_AA64PFR0_EL1_FP)),
 	ID_FILTERED(ID_AA64PFR1_EL1, id_aa64pfr1_el1,
 				     ~(ID_AA64PFR1_EL1_PFAR |
-				       ID_AA64PFR1_EL1_DF2 |
 				       ID_AA64PFR1_EL1_MTEX |
 				       ID_AA64PFR1_EL1_THE |
 				       ID_AA64PFR1_EL1_GCS |