ppc/pegasos2: Use Virtual Open Firmware as firmware replacement

ppc/pegasos2: Use Virtual Open Firmware as firmware replacement

The pegasos2 board comes with an Open Firmware compliant ROM based on
SmartFirmware but it has some changes that are not open source
therefore the ROM binary cannot be included in QEMU. Guests running on
the board however depend on services provided by the firmware. The
Virtual Open Firmware recently added to QEMU implements a minimal set
of these services to allow some guests to boot without the original
firmware. This patch adds VOF as the default firmware for pegasos2
which allows booting Linux and MorphOS via -kernel option while a ROM
image can still be used with -bios for guests that don't run with VOF.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-Id: <1d6ed6f290c5c1f0b5a1e1c51cf1151452d70d9a.1624811233.git.balaton@eik.bme.hu>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>