drm/i915: Set GPU freq to idle_freq initially

drm/i915: Set GPU freq to idle_freq initially

Currently we set the initial GPU frequency to min_freq_softlimit
on gen9, and to efficient_freq on VLV/CHV. On all the other platforms
we set it to idle_freq. Let's use idle_freq across the board to make
sure we don't waste power. This is especially relevant for VLV since
Vnn won't drop to minimum unless the GPU is at the minimum frequency.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1457120584-26080-3-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>