MIPS: Kconfig: Drop obsolete NR_CPUS_DEFAULT_{1,2} options

MIPS: Kconfig: Drop obsolete NR_CPUS_DEFAULT_{1,2} options

The NR_CPUS_DEFAULT_1 introduced as an aid for the QEMU
platform in 72ede9b18967e7a8a62a88f164f003193f6d891f
"[MIPS] Qemu: Fix Symmetric Uniprocessor support"
which was later removed in
302922e5f6901eb6f29c58539631f71b3d9746b8
"[MIPS] Qemu: Remove platform."

On certain randconfigs it may happen for NR_CPUS to have an
empty value because not all SMP platforms select a suitable
NR_CPUS_DEFAULT_* value. We fix this by restoring the range
of NR_CPUS to 2..64 and drop the NR_CPUS_DEFAULT_{1,2} symbols.
The first one is no longer used and the latter is not needed since
NR_CPUS=2 is now the default value.

Fixes the following problem on a randconfig:
.config:164:warning: symbol value '' invalid for NR_CPUS

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5747/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>