PM / devfreq: memlat: Don't ignore extremely latency sensitive workloads

The ratio value that's compared against ratio_ceil tunable can be 0 for
workloads that are extremely latency sensitive. So, we can't ignore cores
that have a ratio of 0 (which was done to ignore idle cores). So, stop
ignoring cores with a ratio of 0 and instead check for instruction or
frequency being 0 to identify idle cores.

Change-Id: I8c6c14f374f016e6612c3b834589d065bad8f488
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>