apcidump: Add dumping SPCR

When we find a SPCR (Serial Port Console Redirection) TABLE, print all
the details. This includes support for the recent Revision 3 and
Revision 4 tables, though I've not encountered them in the wild yet, so
that code is untested.

https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table

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