tests: Add cgpt fuzzer. This adds a fuzzer binary to exercise GPT parsing. BUG=chromium:1014101 TEST=Build and run fuzzer. BRANCH=none Change-Id: Idecc0ddf491e976d4e01f5778e51a01ac317d961 Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1859595 Reviewed-by: Julius Werner <[email protected]> Tested-by: Manoj Gupta <[email protected]> Commit-Queue: Manoj Gupta <[email protected]>