Build: Support building IPC model without tests

Refactors the build configuration variables so that the Core IPC tests
are only built if either CORE_TEST or REGRESSION is enabled (as well as
CORE_IPC). This matches the build behaviour for library model.

Adds a TFM_PARTITION_TEST_CORE_IPC build variable to make it possible
to compile-out the Core IPC test partition when the Core IPC tests are
not built.

Removes some unneeded build system behaviour that was conditional on
CORE_TEST to avoid causing problems when CORE_IPC is enabled.

Change-Id: Ia88bd3785817cc2dcedf88b737690fc32cc3266e
Signed-off-by: Jamie Fox <jamie.fox@arm.com>
14 files changed