drm: Add drm_any_plane_has_format()

Add a function to check whether there is at least one plane that
supports a specific format and modifier combination. Drivers can
use this to reject unsupported formats/modifiers in .fb_create().

v2: Accept anyformat if the driver doesn't do planes (Eric)
    s/planes_have_format/any_plane_has_format/ (Eric)
    Check the modifier as well since we already have a function
    that does both
v3: Don't do the check in the core since we may not know the
    modifier yet, instead export the function and let drivers
    call it themselves

Cc: Eric Anholt <eric@anholt.net>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181029183453.28541-1-ville.syrjala@linux.intel.com

include/drm/drm_mode_config.h

@@ -52,6 +52,12 @@ struct drm_mode_config_funcs {
 	 * requested metadata, but most of that is left to the driver. See
 	 * &struct drm_mode_fb_cmd2 for details.
 	 *
+	 * To validate the pixel format and modifier drivers can use
+	 * drm_any_plane_has_format() to make sure at least one plane supports
+	 * the requested values. Note that the driver must first determine the
+	 * actual modifier used if the request doesn't have it specified,
+	 * ie. when (@mode_cmd->flags & DRM_MODE_FB_MODIFIERS) == 0.
+	 *
 	 * If the parameters are deemed valid and the backing storage objects in
 	 * the underlying memory manager all exist, then the driver allocates
 	 * a new &drm_framebuffer structure, subclassed to contain