sched/isolation: Make CONFIG_CPU_ISOLATION=y depend on SMP or COMPILE_TEST

On uniprocessor systems, critical and non-critical tasks cannot be
isolated, as there is only a single CPU core.  Hence enabling CPU
isolation by default on such systems does not make much sense.

Instead of changing the default for !SMP, fix this by making the feature
depend on SMP, with an override for compile-testing.  Note that its sole
selector (NO_HZ_FULL) already depends on SMP.

This decreases kernel size for a default uniprocessor kernel by ca. 1 KiB.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 2c43838c ("sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default")
Link: http://lkml.kernel.org/r/1514891590-20782-1-git-send-email-geert@linux-m68k.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>