lib: os: assert: Avoid including printk.h in __assert.h

Create wrapper for printk to avoid including printk.h in __assert.h.
__assert.h is used everywhere thus should not have dependency to
printk.h.

Cleanup assert Kconfig options.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>