MIPS: Alchemy: update cpu-feature-overrides

No shiny new stuff for Alchemy.

Tested on DB1300 and DB1500.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Linux-MIPS <linux-mips@vger.kernel.org>