[dv] Randomize ROM in chip_base_vseq
[dv] Randomize ROM in chip_base_vseq

Because the rom_ctrl block reads the contents of ROM and passes them
to KMAC (which has X checks), we need it to have *some* architectural
contents. We don't really care what, though, so randomize it here.

Tests that actually have a ROM image use chip_sw_base_vseq, which
loads up the ROM image a bit later.

Signed-off-by: Rupert Swarbrick <290093e2ad2515ed2f14d749293c8cf8e02ca274@lowrisc.org>

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