KVM: PPC: Book3S HV: Return error from h_set_mode(SET_DAWR) on POWER9

Return H_P2 on a h_set_mode(SET_DAWR) on POWER9 where the DAWR is
disabled.

Current Linux guests ignore this error, so they will silently not get
the DAWR (sigh). The same error code is being used by POWERVM in this
case.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/book3s_hv.c

@@ -741,6 +741,8 @@ static int kvmppc_h_set_mode(struct kvm_vcpu *vcpu, unsigned long mflags,
 	case H_SET_MODE_RESOURCE_SET_DAWR:
 		if (!kvmppc_power8_compatible(vcpu))
 			return H_P2;
+		if (!ppc_breakpoint_available())
+			return H_P2;
 		if (mflags)
 			return H_UNSUPPORTED_FLAG_START;
 		if (value2 & DABRX_HYP)