sched: EAS: use busy energy cost when CPU is not in a C-state

When the CPU is idle but not in a C-state, i.e. not in WFI
regardless of its load the CPU's energy cost is proportional to its
frequency rather than static.  However at present energy_diff() tends
to underestimate energy cost of CPU not in a C-state when a CPU's
load is low by assuming energy cost is static.

Use energy cost of CPU frequency rather than static idle cost when CPU
is not in a C-state.

Change-Id: I63060be34652f3a1e8f85eca235440e033e614ee
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>