cpufreq: schedutil: Change to using WALT load

WALT load works better for UX workloads which are important for a
commercial mobile device.

Change-Id: I33fbb5c0566176288029e3249532f8c4b389add3
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>