drm/i915: sync hdmi detection by hdmi identifier with 2D

Currently we detect HDMI monitor by hardware detection, but if an HDMI-DVI
adapter is used to connect a DVI monitor, hardware detection will incorrectly
take monitor as HDMI. HDMI spec says any device containing IEEE registration
identifier will be treated as HDMI device.  The patch intends to detect HDMI
monitor by drm_detect_hdmi_monitor function which follows that rule.

Signed-off-by: Ma Ling <ling.ma@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>