Patch from Christoph Hellwig

It turns alloc_pages_node into a static inline, in the same fashion as
alloc_pages.  There is no need for #ifdef CONFIG_NUMA in the patch, as
the numa node identification functions are sensible enough to do the
right thing for non-NUMA systems.  Moves alloc_pages_node from numa.c
to gfp.h, and removes the EXPORT_SYMBOL which is no longer needed as
this is now an inline.