kernel: init: simplify boot banner printing

Just use printk directly instead of going over defines.

For some reason, this change lets us pass on master when running
tests/kernel/timer/timer_monotonic test. This test started failing after
rc2 was tagged, just because the changing git version string passing to
BUILD_VERSION. This is still under investigation.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>