microblaze: fix musl support

microblaze: fix musl support

For musl we need patches for bintils 2.25.1 and 2.26.1.
Binutils 2.27 and gcc 6.2.x does not work for microblaze,
even not for uClibc-ng or glibc.
For gcc 5.4.x the existing patch need reworking so that
musl and uClibc-ng is supported.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
[Thomas:
 - Add proper description for the binutils patches
 - Use BR2_microblaze instead of BR2_microblazeel and BR2_microblazebz]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>