Michael Brown
38cd351243
[romprefix] Attempt to gracefully handle semi-PnP IBM BIOSes
Some IBM BIOSes provide partial support for PnP: they will use the BEV
entry point but will not advertise PnP support. This causes iPXE to
hook INT 19, which disrupts the boot process.
Attempt to improve this situation by detecting an IBM BIOS and
treating it as a PnP BIOS despite the absence of a PnP signature.
Signed-off-by: Michael Brown <mcb30@ipxe.org>