OpenGL2: Use CPU vertex animation if too few vertex attributes

OpenGL ES has a minimum of 8 vertex attributes while desktop OpenGL has
a minimum of 16. Vertex animation uses attributes 10 to 12.

code/renderergl2/tr_local.h

@@ -1433,6 +1433,9 @@ typedef struct {
 	qboolean vertexArrayObject;
 	qboolean directStateAccess;
 
+	int maxVertexAttribs;
+	qboolean gpuVertexAnimation;
+
 	GLenum vaoCacheGlIndexType; // GL_UNSIGNED_INT or GL_UNSIGNED_SHORT
 	size_t vaoCacheGlIndexSize; // must be <= sizeof( vaoCacheGlIndex_t )