intel_idle: add Sierra Forest SoC support

Add Sierra Forest SoC C-states, which are C1, C1E, C6S, and C6SP.

Sierra Forest SoC is built with modules, each module includes 4 cores
(Crestmont microarchitecture). There is one L2 cache per module, shared
between the 4 cores.

There is no core C6 state, but there is C6S state, which has module scope:
when all 4 cores request C6S, the entire module (4 cores + L2 cache)
enters the low power state.

C6SP state has package scope - when all modules in the package enter C6S,
the package enters the power state mode.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>