MIPS: Alchemy: Update cpu-feature-overrides

More features the Au1 core definitely doesn't have.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/7562/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>