powerpc/mm/radix: Avoid flushing the PWC on every flush_tlb_range

powerpc/mm/radix: Avoid flushing the PWC on every flush_tlb_range

BugLink: http://bugs.launchpad.net/bugs/1709220
We do that because it's used by THP pmd collapsing, so use
instead a dedicated flush function.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit 424de9c6e3f89399fc11afc1f53f89c5329132da linux-next)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>