sim: Add explicit copyright and licenses to the sim

Add an apache SPDX header and explicit license lines.  The date ranges
of the license lines is derived from the git history.  Having these
explicitly present will make contributions from other parties easier, as
they will simply be able to add their own copyright line, rather than
having to describe that it only covers modifications.

Signed-off-by: David Brown <david.brown@linaro.org>