kvmtool, seabios: Ignore BIOS POST legacy registers

This makes SeaBIOS limp along all the way to boot menu:

  [penberg@tux kvm]$ ./vm run --firmware /usr/share/seabios/bios.bin
    # lkvm run -k ../../arch/x86/boot/bzImage -m 448 -c 4 --name guest-11658
  Start bios (version 0.6.0)
  Unable to unlock ram - bridge not found
  Ram Size=0x00100000 (0x0000000000000000 high)
  CPU Mhz=13
  Found 1 cpu(s) max supported 1 cpu(s)
  PCI: bus=0 devfn=0x08: vendor_id=0x1af4 device_id=0x1009
  PCI: bus=0 devfn=0x10: vendor_id=0x1af4 device_id=0x1009
  PCI: bus=0 devfn=0x18: vendor_id=0x1af4 device_id=0x1000
  region 0: 0x00000000
  region 1: 0x00000000
  WARNING - Unable to allocate resource at mptable_init:26!
  WARNING - Unable to allocate resource at smbios_init:381!
  Scan for VGA option rom
  WARNING - Timeout at i8042_wait_read:35!
  Found 2 lpt ports
  Found 4 serial ports
  Scan for option roms
  Press F12 for boot menu.

Signed-off-by: Pekka Enberg <penberg@kernel.org>