Decompress PEI modules

[rjoleary]

The FVFileTypePEIM line was commented out in supportedFiles to prevent PEI sections from being compressed. This was necessary because PEI sections would re-compress to a larger size and overflow the PEI firmware volume.

To fix this, only sections which have been changed should be re-compressed. It might be possible to implement this with dirty bits, diffing or hashing.