sched/isolation: Make CONFIG_CPU_ISOLATION depend on CONFIG_SMP

kernel/sched/isolation.c obviously makes no sense without CONFIG_SMP, but
the Kconfig entry we have right now:

config CPU_ISOLATION
bool "CPU isolation"
depends on SMP || COMPILE_TEST

allows the creation of pointless .config's which cause
build failures.

Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Oleg Nesterov <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/

init/Kconfig

···
 
 config CPU_ISOLATION
 	bool "CPU isolation"
-	depends on SMP || COMPILE_TEST
+	depends on SMP
 	default y
 	help
 	  Make sure that CPUs running critical tasks are not disturbed by