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 <[e-mail]>
Signed-off-by: Darren Stevens <[e-mail]>
Reviewed-by: Aneesh Kumar K.V <[e-mail]>
[mpe: Add #ifdef CONFIG_PCI, massage change log slightly]
Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/include/asm/book3s/64/pgtable.h

···
 #define KERN_VIRT_SIZE  __kernel_virt_size
 extern struct page *vmemmap;
 extern unsigned long ioremap_bot;
+extern unsigned long pci_io_base;
 #endif /* __ASSEMBLY__ */
 
 #include <asm/book3s/64/hash.h>

arch/powerpc/kernel/pci_64.c

···
 
 	printk(KERN_INFO "PCI: Probing PCI hardware\n");
 
-	pci_io_base = ISA_IO_BASE;
 	/* For now, override phys_mem_access_prot. If we need it,g
 	 * later, we may move that initialization to each ppc_md
 	 */

arch/powerpc/mm/hash_utils_64.c

···
 	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.

arch/powerpc/mm/pgtable-radix.c

···
 	__vmalloc_end = RADIX_VMALLOC_END;
 	vmemmap = (struct page *)RADIX_VMEMMAP_BASE;
 	ioremap_bot = IOREMAP_BASE;
+
+#ifdef CONFIG_PCI
+	pci_io_base = ISA_IO_BASE;
+#endif
+
 	/*
 	 * For now radix also use the same frag size
 	 */