arm64/mpam: Fix repeated enabling in mpam_enable()

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I9AZFU



--------------------------------

In mpam_enable(), the enabling process is designed to be called once after
all devices are probed. But if the kworker is parallel and delayed, it may
be called multi times, add an atomic guard to avoid this situation.

Fixes: e4173244 ("arm64/mpam: Probe supported partid/pmg ranges from devices")
Signed-off-by: Wei Li <liwei391@huawei.com>