drm/amd/display: Allow constructing DCE8 link encoder without DDC

When the DDC channel ID is set to CHANNEL_ID_UNKNOWN,
pass NULL to the AUX regs array.

This is necessary to support embedded connectors without DDC.

Fixes: 4562236 ("drm/amd/dc: Add dc display driver (v2)")
Link: https://gitlab.freedesktop.org/drm/amd/-/work_items/5192
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 155baf3)

Author: Timur Kristóf

drivers/gpu/drm/amd/display/dc/resource/dce80/dce80_resource.c

@@ -760,7 +760,8 @@ static struct link_encoder *dce80_link_encoder_create(
 				      enc_init_data,
 				      &link_enc_feature,
 				      &link_enc_regs[link_regs_id],
-				      &link_enc_aux_regs[enc_init_data->channel - 1],
+				      enc_init_data->channel == CHANNEL_ID_UNKNOWN ?
+				      NULL : &link_enc_aux_regs[enc_init_data->channel - 1],
 				      enc_init_data->hpd_source >= ARRAY_SIZE(link_enc_hpd_regs) ?
 				      NULL : &link_enc_hpd_regs[enc_init_data->hpd_source]);
 	return &enc110->base;