amdgpu/dc: remove various variables that are defined but never used

There are several variables that are defined and never used and hence can
be removed. Remove them. Cleans up clang -Wunused-const-variable warnings:

warning: ‘dvi_hdmi_dongle_signature_str’ defined but not used
warning: ‘dce11_one_lpt_channel_max_resolution’ defined but not used
warning: ‘ddc_hw_status_addr’ defined but not used
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c

@@ -42,7 +42,6 @@
 #define CV_SMART_DONGLE_ADDRESS 0x20
 /* DVI-HDMI dongle slave address for retrieving dongle signature*/
 #define DVI_HDMI_DONGLE_ADDRESS 0x68
-static const int8_t dvi_hdmi_dongle_signature_str[] = "6140063500G";
 struct dvi_hdmi_dongle_signature_data {
 	int8_t vendor[3];/* "AMD" */
 	uint8_t version[2];

drivers/gpu/drm/amd/display/dc/dce110/dce110_compressor.c

@@ -62,8 +62,6 @@ static const struct dce110_compressor_reg_offsets reg_offsets[] = {
 }
 };
 
-static const uint32_t dce11_one_lpt_channel_max_resolution = 2560 * 1600;
-
 static uint32_t align_to_chunks_number_per_line(uint32_t pixels)
 {
 	return 256 * ((pixels + 255) / 256);

drivers/gpu/drm/amd/display/dc/i2caux/dce80/i2c_sw_engine_dce80.c

@@ -50,16 +50,6 @@
  * This unit
  */
 
-static const uint32_t ddc_hw_status_addr[] = {
-	mmDC_I2C_DDC1_HW_STATUS,
-	mmDC_I2C_DDC2_HW_STATUS,
-	mmDC_I2C_DDC3_HW_STATUS,
-	mmDC_I2C_DDC4_HW_STATUS,
-	mmDC_I2C_DDC5_HW_STATUS,
-	mmDC_I2C_DDC6_HW_STATUS,
-	mmDC_I2C_DDCVGA_HW_STATUS
-};
-
 /*
  * @brief
  * Cast 'struct i2c_sw_engine *'