Move state trans fns into state_processing

eth2/state_processing/src/common/verify_bitfield.rs

@@ -0,0 +1,20 @@
+use types::*;
+
+/// Verify ``bitfield`` against the ``committee_size``.
+///
+/// Is title `verify_bitfield` in spec.
+///
+/// Spec v0.4.0
+pub fn verify_bitfield_length(bitfield: &Bitfield, committee_size: usize) -> bool {
+    if bitfield.num_bytes() != ((committee_size + 7) / 8) {
+        return false;
+    }
+
+    for i in committee_size..(bitfield.num_bytes() * 8) {
+        if bitfield.get(i).unwrap_or(false) {
+            return false;
+        }
+    }
+
+    true
+}