drm/displayid: add separate drm_displayid.c

We'll be adding more DisplayID specific functions going forward, so
start off by splitting out a few functions to a separate file.

We don't bother with exporting the functions; at least for now they
should be needed solely within drm.ko.

No functional changes.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/07942d5011891b8e8f77245c78b34f4af97a9315.1617024940.git.jani.nikula@intel.com

include/drm/drm_displayid.h

@@ -22,6 +22,10 @@
 #ifndef DRM_DISPLAYID_H
 #define DRM_DISPLAYID_H
 
+#include <linux/types.h>
+
+struct edid;
+
 #define DATA_BLOCK_PRODUCT_ID 0x00
 #define DATA_BLOCK_DISPLAY_PARAMETERS 0x01
 #define DATA_BLOCK_COLOR_CHARACTERISTICS 0x02
@@ -100,4 +104,8 @@ struct displayid_detailed_timing_block {
 	     (idx) += sizeof(struct displayid_block) + (block)->num_bytes, \
 	     (block) = (const struct displayid_block *)&(displayid)[idx])
 
+const u8 *drm_find_displayid_extension(const struct edid *edid,
+				       int *length, int *idx,
+				       int *ext_index);
+
 #endif

include/drm/drm_edid.h

@@ -543,5 +543,8 @@ struct drm_display_mode *drm_mode_find_dmt(struct drm_device *dev,
 struct drm_display_mode *
 drm_display_mode_from_cea_vic(struct drm_device *dev,
 			      u8 video_code);
+const u8 *drm_find_edid_extension(const struct edid *edid,
+				  int ext_id, int *ext_index);
+
 
 #endif /* __DRM_EDID_H__ */