Add SUBGRAPH_ERROR_IF() to catch graph-level error.

- Also replace SIMPLE_FATAL_ERROR() with FATAL_ERROR() since they're duplicate
- Replace FATAL_ERROR()/ASSERT_MSG() with ERROR_IF_SUBGRAPH() if the condition is a graph error
  FATAL_ERROR()/ASSERT() should only be used by model internal/runtime error like file reading.

Signed-off-by: Kevin Cheng <kevin.cheng@arm.com>
Change-Id: If1e1e2488054a0ecd800fb0f2ea6487019282500