powerpc/perf: Avoid spurious PMU interrupts after idle

powerpc/perf: Avoid spurious PMU interrupts after idle

BugLink: http://bugs.launchpad.net/bugs/1709352
POWER9 DD2 can see spurious PMU interrupts after state-loss idle in
some conditions.

A solution is to save and reload MMCR0 over state-loss idle.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Tested-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit 101dd590a7fa37954540cf3149a1c502c0acc524)
Signed-off-by: Rodrigo R. Galvao <rosattig@linux.vnet.ibm.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>