drm/amd/display/dc/dc_hdmi_types: Move string definition to the only file it's used in

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/../display/dc/dc_hdmi_types.h:53:22:
   warning: ‘dp_hdmi_dongle_signature_str’ defined but not used [-Wunused-const-variable=]

[snipped 400 similar lines for brevity]

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Wenjing Liu <wenjing.liu@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dc_hdmi_types.h

@@ -50,7 +50,6 @@ struct dp_hdmi_dongle_signature_data {
 
 /* DP-HDMI dongle slave address for retrieving dongle signature*/
 #define DP_HDMI_DONGLE_ADDRESS 0x40
-static const uint8_t dp_hdmi_dongle_signature_str[] = "DP-HDMI ADAPTOR";
 #define DP_HDMI_DONGLE_SIGNATURE_EOT 0x04
 
 

drivers/gpu/drm/amd/display/dc/link/link_detection.c

@@ -60,6 +60,8 @@
  */
 #define LINK_TRAINING_MAX_VERIFY_RETRY 2
 
+static const uint8_t dp_hdmi_dongle_signature_str[] = "DP-HDMI ADAPTOR";
+
 static enum ddc_transaction_type get_ddc_transaction_type(enum signal_type sink_signal)
 {
 	enum ddc_transaction_type transaction_type = DDC_TRANSACTION_TYPE_NONE;