util: Add a "semi" call type unit test to the m5 utility.

util: Add a "semi" call type unit test to the m5 utility.

This is largely similar to the "inst" call type test since it's also
another form of illegal instruction, but there's more checking to do
since the way arguments are passed is more complex.

Change-Id: Ie61bb4da8befab579c3044fd2ddee753926de174
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27749
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>