powerpc/mm: Make k(un)map_atomic out of line

Those functions are way too big to be inline, besides, kmap_atomic()
wants to call debug_kmap_atomic() which isn't exported for modules
and causes module link failures.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/mm/Makefile b/arch/powerpc/mm/Makefile
index 2d2192e..3e68363 100644
--- a/arch/powerpc/mm/Makefile
+++ b/arch/powerpc/mm/Makefile
@@ -30,3 +30,4 @@
 obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
 obj-$(CONFIG_PPC_SUBPAGE_PROT)	+= subpage-prot.o
 obj-$(CONFIG_NOT_COHERENT_CACHE) += dma-noncoherent.o
+obj-$(CONFIG_HIGHMEM)		+= highmem.o