use sha512sum to check downloads, not sha1sum

sha-1 has known collision issues, which may not be readily
exploitable yet (in our context), but we should ideally use
a more secure method for checking file integrity.

therefore, use sha-2 (sha512sum) for checking files. this is
slower than sha-1, but checksum verification is only a minor
part of what lbmk does, so the overall effect on build times
is quite negligible.

Signed-off-by: Leah Rowe <leah@libreboot.org>

script/update/blobs/download

@@ -455,7 +455,7 @@ vendor_checksum()
 		printf "Vendor update not found on disk for: %s\n" "${board}" \
 		    1>&2
 		return 1
-	elif [ "$(sha1sum ${dl_path} | awk '{print $1}')" != "${1}" ]; then
+	elif [ "$(sha512sum ${dl_path} | awk '{print $1}')" != "${1}" ]; then
 		printf "Bad checksum on vendor update for: %s\n" "${board}" 1>&2
 		return 1
 	fi