cpufreq: schedutil: Only apply single core busy logic with PELT

Currently, sugov_update_single will apply its busy logic, keeping frequency
high.  However, this is only required for PELT, not WALT; remove this
logic if PELT is not in use.

Change-Id: Ia0d9523d683568e373fa0d459eecbd3fae78fcff
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>