16G and multi size hugetlb page support on powerpc

This patch set builds on Nick Piggin's patches for multi size and giant 
hugetlb page support of April 22.  The following set of patches adds 
support for 16G huge pages on ppc64 and support for multiple huge page 
sizes at the same time on ppc64.  Thus allowing 64K, 16M, and 16G huge 
pages given a POWER5+ or later machine.

New to this version of my patch is numerous bug fixes and cleanups, but 
the biggest change is the support for multiple huge page sizes on power.

patch 1: changes to generic hugetlb to enable 16G pages on power
patch 2: powerpc: adds function for allocating 16G pages
patch 3: powerpc: setups 16G page locations found in device tree
patch 4: powerpc: page definition support for 16G pages
patch 5: check for overflow when user space is 32bit
patch 6: powerpc: multiple huge page size support

Jon