powerpc: Initialise pci_io_base as early as possible

Commit d6a9996e84ac ("powerpc/mm: vmalloc abstraction in preparation for
radix") turned kernel memory and IO addresses from #defined constants to
variables initialised at runtime.

On PA6T (pasemi) systems the setup_arch() machine call initialises the
onboard PCI-e root-ports, and uses pci_io_base to do this, which is now
before its value has been set, resulting in a panic early in boot before
console IO is initialised.

Move the pci_io_base initialisation to the same place as vmalloc ranges
are set (hash__early_init_mmu()/radix__early_init_mmu()) - this is the
earliest possible place we can initialise it.

Fixes: d6a9996e84ac ("powerpc/mm: vmalloc abstraction in preparation for radix")
Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: Darren Stevens <darren@stevens-zone.net>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[mpe: Add #ifdef CONFIG_PCI, massage change log slightly]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 5b22ba0..2971ea1 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -922,6 +922,10 @@
 	vmemmap = (struct page *)H_VMEMMAP_BASE;
 	ioremap_bot = IOREMAP_BASE;
 
+#ifdef CONFIG_PCI
+	pci_io_base = ISA_IO_BASE;
+#endif
+
 	/* Initialize the MMU Hash table and create the linear mapping
 	 * of memory. Has to be done before SLB initialization as this is
 	 * currently where the page size encoding is obtained.