cpufreq_schedutil: Refactor sugov_cpu_is_busy()

sugov_cpu_is_busy() is used to avoid decreasing performance level while the
CPU is busy and called by sugov_update_single_freq() and
sugov_update_single_perf(). Both callers repeat the same pattern to first
test for uclamp and then the business. Let's refactor so that the tests
aren't repeated.

The new helper is named sugov_hold_freq() and tests both the uclamp
exception and CPU business. No functional changes. This will make adding
more exception conditions easier.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: David Vernet <dvernet@meta.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>