Implement interruptible ECC Key Generation (iop tests)

[paul-elliott-arm]

Stage 3 of implementing interruptible ECC key generation.

This would involve implementing psa_generate_key_iop_get_num_ops() and should include tests for the interaction with the iop key generation functions and psa_interruptible_set_max_ops(), for example testing that the max ops set is not exceeded under any condition.