drm/i915: Shovel hw setup code out of ilk_crtc_mode_set

drm/i915: Shovel hw setup code out of ilk_crtc_mode_set

Again this code just transforms sw state from the pipe config into
hardware state, so we can just move it around. Unfortunately again a
few forward declarations since intel_display.c is becoming a bit of a
mess.

Note that both for i9xx and ironlake code the only things remaining in
the ->crtc_mode_set hook is now the clock state computation and
sharing code. That needs to be moved into the compute config stage so
that we can catch impossible configurations earlier.

Also note that some of the DPLL hw setup code is still run from within
->crtc_mode_set, namele the pll->mode_set callback. We need to move
that first before we can do fancy things like enable runtime PM for
dpms off.

v2: Make it compile again after the rebase, bisectability issue
reported by Wu Fengguang.

Reviewed-by: Shobhit Kumar <shobhit.kumar@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>