feat(tftf): refactoring of some tftf function helpers

This refactoring is introduced in order to reuse some useful
function helpers which already exist in the code base,
by moving one function to test_helpers.c

Signed-off-by: Nabil Kahlouche <nabil.kahlouche@arm.com>
Change-Id: If5c24da9062d100419220fe000409b73596e773c
4 files changed