Remove PowerPC architecture

The PPC port is incomplete and unmaintained so remove it.  It's more
productive to spend time on the LLVM backend or the interpreter for
anyone wanting to run Jato on PowerPC.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
Remove ARM architecture

The ARM port is incomplete and unmaintained so remove it.  It's more
productive to spend time on the LLVM backend or the interpreter for
anyone wanting to run Jato on ARM.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
Update README

Signed-off-by: Pekka Enberg <penberg@kernel.org>