tests_reg: Add test for refused connection in SFN

Add tfm_sfn_test_1008 test case to check the correct PSA_ERROR
returned value from a RoT which refuses a connection with the
SFN backend.

Signed-off-by: Nicola Mazzucato <nicola.mazzucato@arm.com>
Change-Id: Ib695ee67de55fc232ceaeb5f3312d4f08abe10b1
6 files changed