prep: Update ppc_rom.bin

Functionally, this is a revert of Jocelyn's r3309 /
55aa45ddde3283cdd781326d001f7456bf02f684 (Quickly hack PowerPC BIOS
able to boot on CDROM again.), for which we do not have the sources.

Therefore the sources used are v0.4.1 plus pc-bios/ohw.diff plus a
workaround turning IDE errors into warnings.

Signed-off-by: Andreas Färber <andreas.faerber@web.de>
