graphicsdriver/opengl: Exclude bytes.go from non-mobile environments

This requires reflect and reflect prevents Ebiten from being compiiled
with TinyGo.

Updates #747

internal/graphicsdriver/opengl/bytes.go

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build android ios
+
 package opengl
 
 import (