drm/i915: extract intel_tv.h from intel_drv.h

It used to be handy that we only had a couple of headers, but over time
intel_drv.h has become unwieldy. Extract declarations to a separate
header file corresponding to the implementation module, clarifying the
modularity of the driver.

Ensure the new header is self-contained, and do so with minimal further
includes, using forward declarations as needed. Include the new header
only where needed, and sort the modified include directives while at it
and as needed.

No functional changes.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f44c21e3d154e47233ebef4267ce1a924fa38df7.1554461791.git.jani.nikula@intel.com

drivers/gpu/drm/i915/intel_drv.h

@@ -2082,9 +2082,6 @@ static inline bool icl_is_hdr_plane(struct drm_i915_private *dev_priv,
 	return plane_id < PLANE_SPRITE2;
 }
 
-/* intel_tv.c */
-void intel_tv_init(struct drm_i915_private *dev_priv);
-
 /* intel_atomic.c */
 int intel_digital_connector_atomic_get_property(struct drm_connector *connector,
 						const struct drm_connector_state *state,