ml-apps: Add helper libraries

In order for ML applications to access the API headers for the
ML Evaluation Kit libraries, various paths in the
ML Embedded Evaluation Kit's source directory need to be made
available to them as include directories.

Helper libraries have been created with library archives and
include directories added to those helper libraries. ML applications
will link the helper libraries they need, in order to inherit the
library archives for linking and include directories for API headers.

Signed-off-by: Hugues Kamba-Mpiana <hugues.kambampiana@arm.com>
Signed-off-by: Ahmed Ismail <Ahmed.Ismail@arm.com>