drm/i915: Set up a render context on Ironlake

RC6 power state requires a logical render context in place for saving
render context.

Signed-off-by: Zou Nan hai <nanhai.zou@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

diff --cc drivers/gpu/drm/i915/i915_drv.h
Simple merge

diff --cc drivers/gpu/drm/i915/i915_reg.h
Simple merge

diff --cc drivers/gpu/drm/i915/intel_display.c
Simple merge