Add meta-python and e300 BSP to the layer config.

Signed-off-by: Philip Balister <philip@balister.org>
Default to building for E300 by default. Set image fstypes.

meta-xilinx builds a bunch of image types. If you build a large image, you
will run out of disk space. Force IMAGE_FSTYPES to only build tar.gz since
that is what most people will need.

Signed-off-by: Philip Balister <philip@balister.org>