repart: Allow combining CopyBlocks= and CopyFiles=

repart: Allow combining CopyBlocks= and CopyFiles=

Let's allow the combination of these two options. When used, repart
will first try to apply the CopyBlocks= behavior. If that's not possible,
it falls back to the CopyFiles= behavior.

This is a first step in being able to also use the partition definition
files shipped in the image to build the image in mkosi instead of having
a separate set of repart definition files to build the image.