Gallery: speed up TileImageView

For a 1920x1080 screen, 40 256x256 tiles are needed. However, tile
uploading is limited to 1 tile per frame, which will last for 40
frames in this case. Remove the limit and use available time in
onGLIdle().

Change-Id: I688a158dff0c03aca2d7f063df6134b0ffc0b08a
CRs-Fixed: 962597