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/include/transfer_list.h b/include/transfer_list.h
index 1e4bd7b..0d9b5a3 100644
--- a/include/transfer_list.h
+++ b/include/transfer_list.h
@@ -9,6 +9,7 @@
 
 #include <assert.h>
 #include <stdbool.h>
+#include <stddef.h>
 #include <stdint.h>
 
 #define TRANSFER_LIST_SIGNATURE 0x4a0fb10b
@@ -163,5 +164,9 @@
 struct transfer_list_entry *transfer_list_find(struct transfer_list_header *tl,
 					       uint32_t tag_id);
 
+struct entry_point_info *
+transfer_list_set_handoff_args(struct transfer_list_header *tl,
+			       struct entry_point_info *ep_info);
+
 #endif /* __ASSEMBLER__ */
 #endif /* TRANSFER_LIST_H */