get_blobs: extract blobs from precompiled Purism coreboot images
Rather than download large repositories of files from sources we don't control and patch files as needed, simply extract the files from precompiled, known good Purism coreboot images.
This offers multiple advantages:
- single source for all blobs, which we control
- significantly smaller download requirements for end user
- significantly less script complexity
- much, much faster
Signed-off-by: Matt DeVillier email@example.com