powerpc/fsl-booke: Fix comments in mmu code that mention BATS

There are no BATS on BookE - we have the TLBCAM instead.  Also correct
the page size information to included extended sizes.  We don't actually allow
a 4G page size to be used, so comment on that as well.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>