cpufreq: schedutil: Avoid processing certain notifications

Prevent processing notifications from scheduler for pl if pl is
not enabled.

Change-Id: I091ee107af21fe94177e0bd051f8ee546f3a1678
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
[avilaj@codeaurora.org: Fix some merge conflicts.]
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>