arch: arm: Define & implement API for test target (Non-Secure)

This commit defines and implements an internal ARMv8-M API
that allows the user to evaluate access permissions of memory
locations, based on the ARMv8-M Test Target (TT) instruction
support.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>