number in the irq register. While there are other issues with these
variants, avoiding writing to it helps interrupt generation on at
least one card, and doesn't hurt on the others. Flag ISA attachment
as needing INT_NO_REG written, and don't update the PC Card attachment
(which will have the effect of not touching it for PC Cards).
Document this in a comment, and tweak one or two formatting nits while
I'm here.
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