powerpc/e6500: Optimize hugepage TLB misses

Some workloads take a lot of TLB misses despite using traditional
hugepages.  Handle these TLB misses in the asm fastpath rather than
going through a bunch of C code.  With this patch I measured around a
5x speedup in handling hugepage TLB misses.

Signed-off-by: Scott Wood <scottwood@freescale.com>