[coreboot] AMD Serengeti Cheetah devices

[Myles Watson]

I'm trying to undertand dts better, and found this.  This patch removes
extra devices from the v2 Config.lb file for serengeti cheetah.

The only change without these devices is that now these lines are missing
from the log:

Disabling static device: PCI: 00:19.0
Disabling static device: PCI: 00:19.1
Disabling static device: PCI: 00:19.2
Disabling static device: PCI: 00:19.3

Signed-off-by: Myles Watson

Thanks,
Myles