drm/i915/glk: Fix DMC/DC state idleness calculation

drm/i915/glk: Fix DMC/DC state idleness calculation

According to BSpec GLK like BXT needs to ignore the idle state of cores
before starting the DMC firmware's DC state handler.

Fixes: dbb28b5c3d3c ("drm/i915/DMC/GLK: Load DMC on GLK")
Cc: Anusha Srivatsa <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Signed-off-by: Imre Deak <[email protected]>
Reviewed-by: Rodrigo Vivi <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]