tests: arch: arm: do not build/run test suites for _ns boards

Some test suites depend on determining at run-time
an available IRQ line which can then be used to execute
the test suite. This logic cannot used if the available
IRQ line is not targeting the current security state.
Therefore, filter out the _ns Cortex-m boards from
running these tests suites (i.e. when building with
CONFIG_TRUSTED_EXECUTION_NONSECURE=y) since we can not
contol the target state of the NVIC interrupt lines.

These tests suites test generic ARM features, that do
not depend on TrustZone-M configuration, so it is OK
that they are only executed on ARM platforms without
the NONSECURE configration set.

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