Update documentation

Add documentation about how base addresses are used by the driver
unit tests.

Update message handler application to use TENSOR_ARENA_SIZE the
same way as the FreeRTOS application.

Add documenation about Corstone-310.

Change-Id: I08a315b95ca757ce3449cb7af104b8f1ac7f8865
diff --git a/applications/message_handler/main.cpp b/applications/message_handler/main.cpp
index b527840..8db9e0b 100644
--- a/applications/message_handler/main.cpp
+++ b/applications/message_handler/main.cpp
@@ -52,14 +52,14 @@
  ****************************************************************************/
 
 // Nr. of tasks to process inferences with, reserves driver & runs inference (Normally 1 per NPU, but not a must)
-#if defined(ETHOSU_NPU_COUNT)
+#if defined(ETHOSU) && defined(ETHOSU_NPU_COUNT) && ETHOSU_NPU_COUNT > 0
 constexpr size_t NUM_PARALLEL_TASKS = ETHOSU_NPU_COUNT;
 #else
 constexpr size_t NUM_PARALLEL_TASKS = 1;
 #endif
 
 // TensorArena static initialisation
-constexpr size_t arenaSize = TENSOR_ARENA_SIZE / NUM_PARALLEL_TASKS;
+constexpr size_t arenaSize = TENSOR_ARENA_SIZE;
 
 __attribute__((section(".bss.tensor_arena"), aligned(16))) uint8_t tensorArena[NUM_PARALLEL_TASKS][arenaSize];