[coreboot] X201 bootblock unlocking

[Vladimir 'φ-coder/phcoder' Serbinenko]

Hello all. On X201 top 192K are locked. Fortunately the original BIOS
has a way to update this region.
If you extract a X201 image you'll find a lzint compressed file which
makes 192K decompressed. It's the update. In it you can simply replace
74f8d1fe (PR0) with 74f8d0ff (harmless address with the same checksum),
recompress, correct checksum, update, reboot and PR0 is inactive. tools
to do all this were posted previously (x201_analyze and
x201_reconstruct) except compressor. You need compressor at least as
performant as original. I attach here my own version which is about 2%
underperformant. If you want to have a try, be my guest
Otherwise I simply use external flashing.