drm/amd/display: correct alpha_en programming for new pixel format

[why]
for following new format, no alpha
       SURFACE_PIXEL_FORMAT_GRPH_RGB111110_FLOAT/_FIX:
       SURFACE_PIXEL_FORMAT_GRPH_BGR101111_FLOAT/_FIX
       same as case SURFACE_PIXEL_FORMAT_GRPH_ARGB1555:
Signed-off-by: NCharlene Liu <Charlene.Liu@amd.com>
Reviewed-by: NChris Park <Chris.Park@amd.com>
Acked-by: NQingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_dpp.c

@@ -181,9 +181,11 @@ static void dpp2_cnv_setup (
 		break;
 	case SURFACE_PIXEL_FORMAT_GRPH_RGB111110_FIX:
 		pixel_format = 112;
+		alpha_en = 0;
 		break;
 	case SURFACE_PIXEL_FORMAT_GRPH_BGR101111_FIX:
 		pixel_format = 113;
+		alpha_en = 0;
 		break;
 	case SURFACE_PIXEL_FORMAT_VIDEO_ACrYCb2101010:
 		pixel_format = 114;
@@ -199,9 +201,11 @@ static void dpp2_cnv_setup (
 		break;
 	case SURFACE_PIXEL_FORMAT_GRPH_RGB111110_FLOAT:
 		pixel_format = 118;
+		alpha_en = 0;
 		break;
 	case SURFACE_PIXEL_FORMAT_GRPH_BGR101111_FLOAT:
 		pixel_format = 119;
+		alpha_en = 0;
 		break;
 	default:
 		break;