Build: Set ns_agent partition flags

Remove defaults for CONFIG_TFM_USE_TRUSTZONE and
TFM_MULTI_CORE_TOPOLOGY.

Derive TFM_PARTITION_NS_AGENT_MAILBOX and TFM_PARTITION_NS_AGENT_TZ
from other configuration flags, and then use those flags where more
appropriate.

The goal is to open the path to other ns_agent configurations.

Change-Id: Ia866fd43d0cfbbaea0f70c9f9ee200644ce8bf9b
Signed-off-by: Chris Brand <chris.brand@cypress.com>
24 files changed