Gallery: don't use tile for small thumbnails

A thumbnail on an FHD screen is ~380px while tile size is 256px. It's
quite inefficient to upload a thumbnail in 4 such tiles. As devices
today can upload bigger textures in less time, tiling is no longer
needed for small thumbnails.

CRs-Fixed: 1024519
Change-Id: I95f9a5f1c695b7d7f1401b3a294848d46f1c3545