KVM: arm64: Fix missing RES1 in emulation of DBGBIDR

The AArch32 CP14 DBGDIDR has bit 15 set to RES1, which our current
emulation doesn't set. Just add the missing bit.
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/sys_regs.c

@@ -1711,7 +1711,7 @@ static bool trap_dbgidr(struct kvm_vcpu *vcpu,
 		p->regval = ((((dfr >> ID_AA64DFR0_WRPS_SHIFT) & 0xf) << 28) |
 			     (((dfr >> ID_AA64DFR0_BRPS_SHIFT) & 0xf) << 24) |
 			     (((dfr >> ID_AA64DFR0_CTX_CMPS_SHIFT) & 0xf) << 20)
-			     | (6 << 16) | (el3 << 14) | (el3 << 12));
+			     | (6 << 16) | (1 << 15) | (el3 << 14) | (el3 << 12));
 		return true;
 	}
 }