sched/walt: Introduce SCHED_CPUFREQ_CONTINUE for schedutil

Introduce a flag for schedutil to know when cpufreq_update_util() is
called for last cpu in the cluster. This is required so that schedutil
can do only one frequency update for the entire cluster.

Change-Id: I2457b83bca58fdbf5f6c6c0b5eb656204b1d2601
Signed-off-by: Puja Gupta <pujag@codeaurora.org>