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.

Change-Id: I9ec0aeef588cc4f99bb7ca662f9233607a4a84b2
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>