sched: Disable ARCH_POWER feature

Now that scheduler can recognize differences in cpus with regard to
their instructions-per-cycle and/or maximum frequency capabilities,
it can calculate cpu_power of cpus taking those differences into
account. In other words, we don't need to rely on the ARCH_POWER
hook to update cpu_power.

Change-Id: Ie810b6ecc1a746b2ab5d498d6d026d1eb88f959a
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>