powerpc/powernv/npu: Don't explicitly flush nmmu tlb

The nest mmu required an explicit flush as a tlbi would not flush it in the
same way as the core. However an alternate firmware fix exists which should
eliminate the need for this flush, so instead add a device-tree property
(ibm,nmmu-flush) on the NVLink2 PHB to enable it only if required.

Signed-off-by: Alistair Popple <alistair@popple.id.au>
Reviewed-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/pci.h

@@ -187,6 +187,9 @@ struct pnv_phb {
 
 		/* Bitmask for MMIO register usage */
 		unsigned long mmio_atsd_usage;
+
+		/* Do we need to explicitly flush the nest mmu? */
+		bool nmmu_flush;
 	} npu;
 
 #ifdef CONFIG_CXL_BASE