Build: Add MBEDTLS_TARGET_PREFIX

Allows required targets to have prefixes added to them, so that external
projects can avoid target names clashing.

Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index cc68663..580d936 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -1,5 +1,5 @@
 set(libs
-    mbedtls
+    ${mbedtls_target}
 )
 
 # Set the project root directory if it's not already defined, as may happen if
@@ -43,7 +43,7 @@
     add_custom_command(
         OUTPUT test_suite_${data_name}.c
         COMMAND ${MBEDTLS_PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/scripts/generate_test_code.py -f ${CMAKE_CURRENT_SOURCE_DIR}/suites/test_suite_${suite_name}.function -d ${CMAKE_CURRENT_SOURCE_DIR}/suites/test_suite_${data_name}.data -t ${CMAKE_CURRENT_SOURCE_DIR}/suites/main_test.function -p ${CMAKE_CURRENT_SOURCE_DIR}/suites/host_test.function -s ${CMAKE_CURRENT_SOURCE_DIR}/suites --helpers-file ${CMAKE_CURRENT_SOURCE_DIR}/suites/helpers.function -o .
-        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/scripts/generate_test_code.py mbedtls ${CMAKE_CURRENT_SOURCE_DIR}/suites/helpers.function ${CMAKE_CURRENT_SOURCE_DIR}/suites/main_test.function ${CMAKE_CURRENT_SOURCE_DIR}/suites/host_test.function ${CMAKE_CURRENT_SOURCE_DIR}/suites/test_suite_${suite_name}.function ${CMAKE_CURRENT_SOURCE_DIR}/suites/test_suite_${data_name}.data
+        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/scripts/generate_test_code.py ${mbedtls_target} ${CMAKE_CURRENT_SOURCE_DIR}/suites/helpers.function ${CMAKE_CURRENT_SOURCE_DIR}/suites/main_test.function ${CMAKE_CURRENT_SOURCE_DIR}/suites/host_test.function ${CMAKE_CURRENT_SOURCE_DIR}/suites/test_suite_${suite_name}.function ${CMAKE_CURRENT_SOURCE_DIR}/suites/test_suite_${data_name}.data
     )
 
     add_executable(test_suite_${data_name} test_suite_${data_name}.c $<TARGET_OBJECTS:mbedtls_test>)