powerpc/mm/radix: Improve _tlbiel_pid to be usable for PWC flushes

powerpc/mm/radix: Improve _tlbiel_pid to be usable for PWC flushes

BugLink: http://bugs.launchpad.net/bugs/1709220
The PWC flush only needs a single set call, just like the
full (RIC=2) flush.

This will allow us to get rid of the dedicated _tlbiel_pwc()

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 5ce5fe14ed0302315061cf97ce67accd1b25b938 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>