Log: Restore an interface target for logging header

The tfm_ns_log target has been removed but it also carried the
configuration flags for the NS logging. Restore it partially
as an INTERFACE target that is linked to tfm_api_ns which grants
for it to be correctly propagated to all targets that need to
log through the TF-M provided NS interface lib

Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>
Change-Id: I4c188e30dc58f43d7f188c90056199546ed0df8f
diff --git a/app_broker/CMakeLists.txt b/app_broker/CMakeLists.txt
index af42301..3228ea8 100644
--- a/app_broker/CMakeLists.txt
+++ b/app_broker/CMakeLists.txt
@@ -40,6 +40,20 @@
 # lib path
 set(APP_LIB_DIR                  ${CMAKE_CURRENT_LIST_DIR}/../lib)
 
+# TFM NS logging interface
+add_library(tfm_ns_log_msg_interface INTERFACE)
+
+target_include_directories(tfm_ns_log_msg_interface
+    INTERFACE
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/../lib/log>
+        $<INSTALL_INTERFACE:${SPE_INSTALL_INTERFACE_INC}
+)
+
+target_compile_definitions(tfm_ns_log_msg_interface
+    INTERFACE
+        $<$<NOT:$<BOOL:${TFM_NS_LOG_DISABLE}>>:TFM_NS_LOG>
+)
+
 # OS wrapper library consists of the wrapper layer of RTOSes, such as RTX
 add_library(os_wrapper STATIC)
 
@@ -151,6 +165,8 @@
 )
 
 target_link_libraries(tfm_api_ns
+    INTERFACE
+        tfm_ns_log_msg_interface
     PRIVATE
         $<$<BOOL:${TFM_NS_MAILBOX_API}>:tfm_api_ns_mailbox>
         $<$<NOT:$<BOOL:${TFM_NS_MAILBOX_API}>>:tfm_api_ns_tz>