bionic: Add Cortex-A15 optimized version of memcpy

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Add the memcpy implementation from cortex-strings -- faster than
the current implementation on both A9 and A15.

To be investigated: Breaks saving pictures from the camera in
Galaxy Nexus builds

Change-Id: I15fde93282e07626a6e20c092b25c76923513f84
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>