thermal: qpnp-adc-tm: Improve check for pending tasks before suspend

Replace wq_cnt with pm_wakeup_event with 2 seconds to prevent platform
suspend and also add flush workqueue as a part of platform suspend_noirq
to make sure all work is completed prior to platform suspend.

Change-Id: I2741727a2cf00520246497633958da022acfe10d
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>