spinlock: Make SPIN_VALIDATE a Kconfig option.

SPIN_VALIDATE is, as it was previously, enabled per default when having
less than 4 CPUs and either having no flash or a flash size greater than
32kB.

Small targets, which needs to have asserts enabled, can chose to have
the spinlock validation enabled or not and thereby decide whether the
overhead added is acceptable or not.

Signed-off-by: Danny Oerndrup <daor@demant.com>
4 files changed