Use a VBO when drawing blurs

Until now, we were uploading the vertex and uv data for every draw call,
this is not great. This CL created a packed vertex buffer, uploads it
to the graphics card and reuses it.

Test: SurfaceFlinger_tests
Test: manual
Bug: 149792636
Change-Id: Iee72a9a815a8ea43880a21c1b4c61320dea20dff