arm64: Disable early printf if TSLOG

The warning message "ERROR loading DTB" (for systems without a device
tree blob) is printed extremely early in the boot process -- among
other things, before curthread or other pcpu data has been set up.
Unfortunately, printf is instrumented with TSLOG, which cannot run
quite this early.

Wrap the printf in #ifndef TSLOG; the situations where the printf
will be useful are not ones where TSLOG would be in use.