Relicense files for which I am the sole author (as identified by
util/relicense.pl).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

On a 64-bit build, EFI_STATUS codes are 64-bit quantities, with the
"error/warning" bit located in bit 63.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

The low 8 bits of an iPXE error code are currently defined as the
closest equivalent PXE error code.  Generalise this scheme to
platforms other than PC-BIOS by extending this definition to "closest
equivalent platform error code".  This allows for the possibility of
returning meaningful errors via EFI APIs.

Signed-off-by: Michael Brown <mcb30@ipxe.org>