do not set the virtual address to the bus address when the bus
doesn't have either of the PCI_RF_DENSE or PCI_RF_BWX flags set.
The TGA driver uses the virtual address to access the registers,
which on some machines can cause a memory management fault. Map
the bus address as K0SEG virtual memory instead. Note that with
some hardware combinations involving the TGA2 adapter this change
merely results that the memory management fault is replaced by a
machine check.
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