feat(arm): add ep_info handoff args setter

Add support for project specific APIs and re-introduce API for setting
TF-A `entry_point_info` arguments following the Arm register convention.

Change-Id: Ic40ef6d34771fe54b152312779620f22bc106640
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
diff --git a/cmake/ProjectApi.cmake b/cmake/ProjectApi.cmake
new file mode 100644
index 0000000..c0d338a
--- /dev/null
+++ b/cmake/ProjectApi.cmake
@@ -0,0 +1,10 @@
+set(PROJECT_API_SRC_DIR ${PROJECT_SOURCE_DIR}/src/${PROJECT_API})
+set(PROJECT_API_INC_DIR ${PROJECT_SOURCE_DIR}/include/${PROJECT_API})
+
+if(EXISTS "${PROJECT_API_SRC_DIR}")
+    file(GLOB PROJECT_SOURCES "${PROJECT_API_SRC_DIR}/*.c")
+    target_sources(tl PRIVATE ${PROJECT_SOURCES})
+    target_include_directories(tl PUBLIC ${PROJECT_API_INC_DIR})
+else()
+    message(FATAL_ERROR "Project-specific API '${PROJECT_API}' not found")
+endif()