Render DRM-PRIME frames as opaque images

We can't always assume they are NV12. Even if they _are_ NV12,
they may have DRM format modifiers that are incompatible with
simply assuming linear Y and UV buffers (such as tiling).

app/shaders/egl_opaque.vert

@@ -0,0 +1,10 @@
+#version 300 es
+
+layout (location = 0) in vec2 aPosition; // 2D: X,Y
+layout (location = 1) in vec2 aTexCoord;
+out vec2 vTextCoord;
+
+void main() {
+	vTextCoord = aTexCoord;
+	gl_Position = vec4(aPosition, 0, 1);
+}