powerpc/32: Allow __ioremap on RAM addresses for kdump kernel

While for debugging it is good to catch bogus users of ioremap, though
for kdump support it is more convenient to use __ioremap for
copy_oldmem_page() (exactly as we do for PPC64 currently).

Note that copy_oldmem_page() calls __ioremap with flags set to '0',
so it should be safe with the regard to the caches.

The other option is to use kmap_atomic_pfn()[1], but it will not work
for kernels compiled without HIGHMEM.

That is, on a board with 256MB RAM and crashkernel=64M@32M case, the
!HIGHMEM capturing kernel maps 0-96M range, which does not include all
the memory needed to capture the dump. And, obviously, accessing
anything upper than 96M will cause faults.

[1] http://ozlabs.org/pipermail/linuxppc-dev/2007-November/046747.html

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/mm/pgtable_32.c

@@ -173,6 +173,7 @@ __ioremap(phys_addr_t addr, unsigned long size, unsigned long flags)
 	if (p < 16*1024*1024)
 		p += _ISA_MEM_BASE;
 
+#ifndef CONFIG_CRASH_DUMP
 	/*
 	 * Don't allow anybody to remap normal RAM that we're using.
 	 * mem_init() sets high_memory so only do the check after that.
@@ -182,6 +183,7 @@ __ioremap(phys_addr_t addr, unsigned long size, unsigned long flags)
 		       (unsigned long long)p, __builtin_return_address(0));
 		return NULL;
 	}
+#endif
 
 	if (size == 0)
 		return NULL;