remoting: Use DRM FourCC formats instead of GBM formats

The remoting plugin currently has a set_gbm_format() hook, which accepts
GBM_FORMAT_* tokens from the host to set as a supported format.
GBM_FORMAT_* values are strictly aliased with DRM_FORMAT_*.

In order to avoid an extra unnecessary dependency from the remoting
plugin on GBM, switch to using the formats from libdrm instead.

This fixes a compile error seen when the remoting plugin is enabled:

    ../remoting/remoting-plugin.c:39:10: fatal error: gbm.h: No such file or directory
       39 | #include <gbm.h>
          |          ^~~~~~~
    compilation terminated.

The error was caused by not having any dependency at all on GBM from
the remoting backend, which is fixed here by adding a new dependency on
the libdrm headers for drm_fourcc.h.

Signed-off-by: Daniel Stone <daniels@collabora.com>

remoting/meson.build

@@ -10,7 +10,7 @@ if get_option('remoting')
 		'gstreamer-app-1.0', 'gstreamer-video-1.0',
 		'gobject-2.0', 'glib-2.0'
 	]
-	deps_remoting = [ dep_libweston_private ]
+	deps_remoting = [ dep_libweston_private, dep_libdrm_headers ]
 	foreach depname : depnames
 		dep = dependency(depname, required: false)
 		if not dep.found()

remoting/remoting-plugin.c

@@ -36,12 +36,12 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <fcntl.h>
-#include <gbm.h>
 
 #include <gst/gst.h>
 #include <gst/allocators/gstdmabuf.h>
 #include <gst/app/gstappsrc.h>
 #include <gst/video/gstvideometa.h>
+#include <drm_fourcc.h>
 
 #include "remoting-plugin.h"
 #include <libweston/backend-drm.h>
@@ -69,6 +69,8 @@ struct remoted_gstpipe {
 
 /* supported gbm format list */
 struct remoted_output_support_gbm_format {
+	/* GBM_FORMAT_* tokens are strictly aliased with DRM_FORMAT_*, so we
+	 * use the latter to avoid a dependency on GBM */
 	uint32_t gbm_format;
 	const char *gst_format_string;
 	GstVideoFormat gst_video_format;
@@ -76,15 +78,15 @@ struct remoted_output_support_gbm_format {
 
 static const struct remoted_output_support_gbm_format supported_formats[] = {
 	{
-		.gbm_format = GBM_FORMAT_XRGB8888,
+		.gbm_format = DRM_FORMAT_XRGB8888,
 		.gst_format_string = "BGRx",
 		.gst_video_format = GST_VIDEO_FORMAT_BGRx,
 	}, {
-		.gbm_format = GBM_FORMAT_RGB565,
+		.gbm_format = DRM_FORMAT_RGB565,
 		.gst_format_string = "RGB16",
 		.gst_video_format = GST_VIDEO_FORMAT_RGB16,
 	}, {
-		.gbm_format = GBM_FORMAT_XRGB2101010,
+		.gbm_format = DRM_FORMAT_XRGB2101010,
 		.gst_format_string = "r210",
 		.gst_video_format = GST_VIDEO_FORMAT_r210,
 	}