MIPS: Kconfig: Disable MIPS MT and SMP implementations for R6

MIPS: Kconfig: Disable MIPS MT and SMP implementations for R6

R6 does not support the MIPS MT ASE and the CMP/SMP options so
restrict them in order to prevent users from selecting incompatible
SMP configuration for R6 cores. We also disable the CPS/SMP option
because its support hasn't been added to the CPS code yet.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10637/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>