machine_dict: Add i686 to the ELF machine dictionary

machine_dict: Add i686 to the ELF machine dictionary

An error like the following is thrown when building
baremetal applications on some x86 architectures:

  (machine, osabi, abiversion, littleendian, bits) \
    = oe.elf.machine_dict(d)[target_os][target_arch]

Exception: KeyError: i686

Since the i686 (target_arch) key does not exist in the dictionary.

Add the key to fix the error.

Signed-off-by: Alejandro Enedino Hernandez Samaniego <alejandro@enedino.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>