host_shaders: Add copyright headers to OpenGL present shaders

src/video_core/host_shaders/opengl_present.frag

+// Copyright 2020 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
 #version 430 core
 
 layout (location = 0) in vec2 frag_tex_coord;

src/video_core/host_shaders/opengl_present.vert

+// Copyright 2020 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
 #version 430 core
 
 out gl_PerVertex {