mm: oom: ensure emergency trigger is raised before enter into oom

When there is no kill in the system since the last PSI event, the
should_ulmk_retry() returns with out raising the emergency trigger thus
system follows OOM path. Avoid this by making sure that the PSI
emergency trigger is raised in the last ULMK_EMERG_TRIG_TIMEOUT window.

Change-Id: I99754c30c08a04902a2849c051510b371538467a
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>