when we hit a conflict where the pci INTL register gives us
a different irq than we get from southbridge irq router, dont
just change the router setting to the bios assigned irq (that
was previously known as the BIOS workarround), but assume the
southbridge setting to be valid and change the pci INTL register
on the device to it.
only when the router link doesnt seem to be configured or
disabled, then program the router to the irq that bios asisgned
in the INTL register.
the reason is that changing the router setting changes the
irq routing for *all* devices on the same link and changing
it breaks previously checked and valid interrupt routings.
(so happend with virtualbox where the last device on the bus
is some powermanagement device that has wrong INTL setting
and changing the routing breaks the ethernet interrupts)
this change shouldnt affect modern machines which use ioapic
and mp tables or acpi for pci interrupt routing.
replace the various functions that searched for bios data structures by
a single sigsearch() one in pc/memory.c that will probe the various bios
data areas.
also, a new checksum() function was added that is to be used to validate
the structures found.
