cpufreq_conservative: Improve support for micro idle accounting

The minimum samplerate calculations of the current conservative
implementation assume that there is not micro idle accounting present,
however, we do have that capability in our idle estimates.  As a result,
we can support lower polling intervals just like ondemand does.

Change-Id: I134027f28abd8e76ee8212685572272b1ddaa872
Signed-off-by: Andrew Dodd <atd7@cornell.edu>
(cherry picked from commit 4b16826d331d02ccfaae73edd01f8f04476bb763)
Sammy Update 13

(cherry picked from commit 466419b9375d5dc1d59108a66f52441aaedf9e31)