soc/intel_adsp: Remove LOG_PRINTK

This was added early when we had (somewhat oddly) a log subsystem
backend but not a printk char_out hook. Now we have one backend that
works with both.  No need, and this fixes build errors with a handful
of tests that specify LOG_MINIMAL (LOG_PRINTK requires the full log
subsystem and doesn't work with MINIMAL).

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>