MIPS: DEC: Update R3k DECstation defconfig for Y2018

Regenerate the R3k DECstation defconfig, in particular including more
relevant drivers.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20984/
Cc: Ralf Baechle <ralf@linux-mips.org>