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
libc: Add Scorpion-optimized memcpy and memset

 * Optimized routines from Qualcomm for msm8660 class SoCs
 * Enable with TARGET_CPU_VARIANT := scorpion
 * Use cortex-a15 memcpy and krait memset routines

Change-Id: I01d0f22efba5a418ddd20fca0d0c570d855e0f6f