drm: Shrink {width,height}_mm to u16

Instead of supporting ~2000km wide displayes let's limit ourselves
to ~65m. That seems plenty big enough to me.

Even with EDID_QUIRK_DETAILED_IN_CM EDIDs seem to be limited to
10*0xfff which fits into the 16 bits.
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200428171940.19552-6-ville.syrjala@linux.intel.com

include/drm/drm_modes.h

@@ -331,7 +331,7 @@ struct drm_display_mode {
 	 * Addressable size of the output in mm, projectors should set this to
 	 * 0.
 	 */
-	int width_mm;
+	u16 width_mm;
 
 	/**
 	 * @height_mm:
@@ -339,7 +339,7 @@ struct drm_display_mode {
 	 * Addressable size of the output in mm, projectors should set this to
 	 * 0.
 	 */
-	int height_mm;
+	u16 height_mm;
 
 	/**
 	 * @crtc_clock: