The purpose of helpers.c file is to contain the helper
functions that have been in helpers.function so far and
that are not related to the mechanism of unit test
execution and not related to random number generation
(will be moved in a dedicated file).
The purpose of helpers.h is to contain the interface
exposed by helpers.c thus helper function prototypes.
Make the changes in the build systems (make and cmake)
to build helpers.c and link it to test executables
along with mbedtls library.
Signed-off-by: Ronald Cron <ronald.cron@arm.com>