The MMIO trace contains register values for parts of the GPU that are
not modeled in gem5, such as registers related to the graphics core.
Since MI100 and MI200 do not have anything that is not modeled, the
MMIO trace is not needed, therefore it does not need to be used or
checked and the command line option goes away entirely for MI100/200.
Change-Id: I23839db32b1b072bd44c8c977899a99347fc9687