implement a command to read / write GBB flag via servo

[hikalium]

make a wrapper for this:

# (in chroot)
sudo emerge -1 hdctools
sudo flashrom -p raiden_debug_spi:target=AP,serial=0780A02E-8C65B668 -r -i GBB:/tmp/gbb.bin
sudo futility gbb -s --flags=0x40b9 /tmp/gbb.bin /tmp/gbb2.bin
sudo flashrom -p raiden_debug_spi:target=AP,serial=0780A02E-8C65B668 -w -i GBB:/tmp/gbb2.bin --noverify-all