bionic: Add ARMv7 optimized string handling routines

Add ARMv7 - and especially Cortex-A9 - optimized string handling
routines based on the versions found in the cortex-strings library.

Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>
Change-Id: I0423fd58c0a1d16e57b3d9ccd40e66922a1722a9