Revert "Remove the MD5 implementation that was only used by toolbox."

This reverts commit 67401638a92abd52e5896183e851b1b097da07ac.

Added TARGET_NEEDS_BIONIC_MD5 to indicate if a device needs it.
In particular, the Galaxy Nexus RIL breaks without this.

Change-Id: I49f1779566dfeb5093970ed0bbda741919318a83