drm/i915: move modesetting output/encoder code under display/

Add a new subdirectory for display code, and start off by moving
modesetting output/encoder code. Judging by the include changes, this is
a surprisingly clean operation.

v2:
- move intel_sdvo_regs.h too
- use tabs for Makefile	file lists and sort them

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190613084416.6794-2-jani.nikula@intel.com

drivers/gpu/drm/i915/Makefile.header-test

@@ -22,46 +22,27 @@ header_test := \
 	intel_color.h \
 	intel_combo_phy.h \
 	intel_connector.h \
-	intel_crt.h \
 	intel_csr.h \
-	intel_ddi.h \
 	intel_display_power.h \
-	intel_dp.h \
-	intel_dp_aux_backlight.h \
-	intel_dp_link_training.h \
-	intel_dp_mst.h \
 	intel_dpio_phy.h \
 	intel_dpll_mgr.h \
 	intel_drv.h \
-	intel_dsi.h \
-	intel_dsi_dcs_backlight.h \
-	intel_dvo.h \
-	intel_dvo_dev.h \
 	intel_fbc.h \
 	intel_fbdev.h \
 	intel_fifo_underrun.h \
 	intel_frontbuffer.h \
-	intel_gmbus.h \
 	intel_hdcp.h \
-	intel_hdmi.h \
 	intel_hotplug.h \
 	intel_lpe_audio.h \
-	intel_lspcon.h \
-	intel_lvds.h \
 	intel_overlay.h \
-	intel_panel.h \
 	intel_pipe_crc.h \
 	intel_pm.h \
 	intel_psr.h \
 	intel_quirks.h \
 	intel_runtime_pm.h \
-	intel_sdvo.h \
-	intel_sdvo_regs.h \
 	intel_sideband.h \
 	intel_sprite.h \
-	intel_tv.h \
 	intel_uncore.h \
-	intel_vdsc.h \
 	intel_wakeref.h
 
 quiet_cmd_header_test = HDRTEST $@