sched/cpufreq_schedutil: create a function for common steps

There are many callsites that do exactly same steps as

hs_util = freq_to_util(sg_policy,
		sg_policy->tunables->hispeed_freq);
hs_util = mult_frac(hs_util, TARGET_LOAD, 100);

Capture them in a function and change all callsites to use it.

Change-Id: Ie7138de7942c51027309101eb6429208a711da74
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>