Connect kern_tslog.c to the build and add TSLOG / TSLOGSIZE kernel options.

Connect kern_tslog.c to the build and add TSLOG / TSLOGSIZE kernel options.
These are intended for debugging purposes and should not be added to
"generic" kernel configurations since they result in a nontrivial amount
of memory being set aside for this purpose, can break if kernel modules are
unloaded, and can potentially leak a dangerous amount of information about
timestamps used as a source of kernel entropy.