The beige G3 Power Macintosh has a 4MB firmware ROM. Fix the size of
the rom region and fall back to loading a binary image with -bios if
loading ELF image failed. This allows testing emulation with a ROM
image from real hardware as well as using an ELF OpenBIOS image.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20201017155139.5A36A746331@zero.eik.bme.hu>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>