sched/walt: Cleanup cpu_util_freq

Minor cleanup involving the cpu_util_freq_walt/pelt function to help
simplify consolidation of WALT parameters for GKI.
Currently, we have a cpu_util_freq function that calls cpu_util in non-WALT
cases and cpu_util_freq_walt with an additional parameter for WALT cases.
The additional parameter is a WALT related structure. This change removes
the dependency of a non-WALT function on a WALT parameter.

Change-Id: Id2fa2b36abcd019c902b530304e58f85b1c70234
Signed-off-by: Sai Harshini Nimmala <snimmala@codeaurora.org>