Change the heuristic for selection of CMSE in the tools python, so that
a non-TrustZone ARMv8 build can happen.
Ideally we would have more direct flagging in the targets, but this
refines the heuristic so the necessary behaviour can be easily
achieved.
* DOMAIN_NS=1 is based purely on the `-NS` suffix on the core name.
* Enabling CMSE in the compiler and outputting a secure import library
is now enabled when the core doesn't have an `-NS` suffix by either
the target label `TFM` being present or the flag `trustzone` being set.
This covers the existing ARMv8-M behaviour - TF-M builds have the TFM
label, as per its documentation; M2351 secure builds have no explicit
flagging, so we ensure that the M2351_NS target has the trustzone flag
set, and the out-of-tree secure target inherits that.
Kevin Bracey
Oren Cohen
Alexander Zilberkant