Remove ethosu_core_rtos

Move away from building generic rtos INTERFACE library in favour of
using the explict rtos targets for the applications that are using it.

Change-Id: I006d7bd302e7b33fa799d32686475e73d4db3182
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 537e9a7..fcb9605 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -68,7 +68,6 @@
 
 # Build RTOS
 add_subdirectory(rtos)
-target_link_libraries(ethosu_core INTERFACE ethosu_core_rtos)
 
 # Build applications
 add_subdirectory(applications)
diff --git a/rtos/CMakeLists.txt b/rtos/CMakeLists.txt
index 7c15d9e..149779e 100644
--- a/rtos/CMakeLists.txt
+++ b/rtos/CMakeLists.txt
@@ -16,11 +16,8 @@
 # limitations under the License.
 #
 
-add_library(ethosu_core_rtos INTERFACE)
-
-# Include FreeRTOS kernel & link with ethosu_rtos target
-if(CORE_SOFTWARE_RTOS_LOWER STREQUAL "freertos")
+# Include FreeRTOS kernel
+if(CORE_SOFTWARE_RTOS_LOWER STREQUAL "freertos" OR CORE_SOFTWARE_RTOS_LOWER STREQUAL "all")
     set(FREERTOS_KERNEL_PATH "${CMAKE_CURRENT_SOURCE_DIR}/freertos/freertos_kernel" CACHE PATH "Path to FreeRTOS kernel.")
     add_subdirectory(freertos_config)
-    target_link_libraries(ethosu_core_rtos INTERFACE freertos_kernel)
 endif()