util/gl: Add the BPTC-compressed formats to piglit-util-gl

piglit_rgbw_image has a special override for compressed formats to
ensure that when the size of the image is less than the size of a
block then it picks a solid color instead of using four colors. This
patch adds the BPTC formats to this list.

It also modifies piglit_get_compressed_block_size to handle the
formats.
Add the bptc formats to fbo-formats.h
bptc: Add tests using fbo-generatemipmap-formats
texwrap: Add the BPTC formats
compressedteximage: Add tests for the four BPTC formats