[POWERPC] MPIC U3/U4 MSI backend

MPIC U3/U4 MSI backend. Based on code from Segher, heavily hacked by me.
This only deals with MSI on U3/U4 MPICs, aka. CPC 9x5.

If we find a U3/U4 then we enable this backend, ie. take over the ppc_md
MSI hooks. We might need more elaborate logic in future to decide which
backend is enabled.

We need our own irq_chip so that we can do MSI masking/unmasking on
the device itself. We also need to mask explicitly on shutdown to make
sure we don't get bitten by lazy-disable semantics.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/sysdev/Makefile b/arch/powerpc/sysdev/Makefile
index a170205..d161679 100644
--- a/arch/powerpc/sysdev/Makefile
+++ b/arch/powerpc/sysdev/Makefile
@@ -2,7 +2,7 @@
 EXTRA_CFLAGS			+= -mno-minimal-toc
 endif
 
-mpic-msi-obj-$(CONFIG_PCI_MSI)	+= mpic_msi.o
+mpic-msi-obj-$(CONFIG_PCI_MSI)	+= mpic_msi.o mpic_u3msi.o
 obj-$(CONFIG_MPIC)		+= mpic.o $(mpic-msi-obj-y)
 
 obj-$(CONFIG_PPC_INDIRECT_PCI)	+= indirect_pci.o