[MIPS] Viper2: Remove defective support.

A defconfig file and the 10 lines of code (including comments ...) that
are rotting since lmo commit 6516a42dc8b40c6c00010346dd51496125b16644
don't quite make proper support, so let's trash it.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>