platform: nordic_nrf: Split secure and nonsecure test functions

Split the nordic platform secure and non-secure test helper functions
into two separate source files.

Change-Id: Ie30e5216f89110f688a45d8d792ac4741e8f8e85
Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>
3 files changed