lmb: Remove __init from lmb_end_of_DRAM()

We call lmb_end_of_DRAM() to test whether a DMA mask is ok on a machine
without IOMMU, but this function is marked as __init.

I don't think there's a clean way to get the top of RAM max_pfn doesn't
appear to include highmem or I missed (or we have a bug :-) so for now,
let's just avoid having a broken 2.6.31 by making this function
non-__init and we can revisit later.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>