remove frv usage of flush_tlb_pgtables()

frv is the last user in the tree of that dubious hook, and it's my
understanding that it's not even needed.  It's only called by memory.c
free_pgd_range() which is always called within an mmu_gather, and
tlb_flush() on frv will do a flush_tlb_mm(), which from my reading of the
code, seems to do what flush_tlb_ptables() does, which is to clear the
cached PGE.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-By: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>