MIPS: Kconfig: CMP support needs to select SMP as well

MIPS: Kconfig: CMP support needs to select SMP as well

The CMP code is only designed to work with SMP configurations.
Fixes multiple build problems on certain randconfigs:

In file included from arch/mips/kernel/smp-cmp.c:34:0:
arch/mips/include/asm/smp.h:28:0:
error: "raw_smp_processor_id" redefined [-Werror]

In file included from include/linux/sched.h:30:0,
from arch/mips/kernel/smp-cmp.c:22:
include/linux/smp.h:135:0: note: this is the location of the
previous definition

In file included from arch/mips/kernel/smp-cmp.c:34:0:
arch/mips/include/asm/smp.h:57:20:
error: redefinition of 'smp_send_reschedule'

In file included from include/linux/sched.h:30:0,
from arch/mips/kernel/smp-cmp.c:22:
include/linux/smp.h:179:20: note: previous
definition of 'smp_send_reschedule' was here

In file included from arch/mips/kernel/smp-cmp.c:34:0:
arch/mips/include/asm/smp.h: In function 'smp_send_reschedule':
arch/mips/include/asm/smp.h:61:8:
error: dereferencing pointer to incomplete type
[...]

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/5812/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>