The ROM field was originally intended as a future alternate way to load
VBIOS without the ROM being on the disk image. This code path is never
taken for the devices gem5 supports and there is no gem5 implementation.
Deprecate the rom_binary field for this reason.
Similarly, MMIO traces were only used for Vega10. Deprecate this as
Vega10 is now deprecated. The MMIO trace reader is kept as it may still
be useful in the future. It is still the primary way to handle devies
which have graphics capability. None of the devices supported by gem5
have graphics now that Vega10 is deprecated.
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