[POWERPC] Fix powerpc 32-bit resource fixup for 64-bit resources

The 32-bit powerpc resource fixup code uses unsigned longs to do the
offsetting of resources which overflows on platforms such as 4xx where
resources can be 64 bits.

This fixes it by using resource_size_t instead.

However, the IO stuff does rely on some 32 bits arithmetic, so we hack
by cropping the result of the fixups for IO resources with a 32 bits
mask.

This isn't the prettiest but should work for now until we change the
32 bits PCI code to do IO mappings like 64 bits does, within a reserved
are of the kernel address space.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>