[boot] More initrd format changes

CDB seemed to be too simple for the needs of init, and squashfs is too
laden with design choices to work around Linux's APIs. This commit adds
creation of an initrd image of a new format I've called `j6romfs`.

Note that this commit currently does not work! The initrd-reading code
still needs to be added.

scripts/fnv.py

@@ -0,0 +1,17 @@
+"""Python implementation of FNV hashes."""
+
+_FNV1_prime32 = 16777619
+_FNV1_prime64 = 1099511628211
+_FNV1_offset32 = 2166136261
+_FNV1_offset64 = 14695981039346656037
+
+def _fnv1a(offset, prime, mask):
+    def hashfunc(data):
+        h = offset
+        for b in data:
+            h = ((h ^ b) * prime) & mask
+        return h
+    return hashfunc
+
+hash64 = _fnv1a(_FNV1_offset64, _FNV1_prime64, (2**64)-1)
+hash32 = _fnv1a(_FNV1_offset32, _FNV1_prime32, (2**32)-1)