MIPS: config: Enable MSA and virtualization for MIPS64R6

All MIPS64R6 cores so far supports MSA and vz, so it makes sense
to enable them in 64R6 default config.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>