refactor: move `inc/hf/arch/plat/ffa` to `inc/hf/ffa`

Change-Id: I05c2cd1aa3753cd60021015c4582831eb03db3c9
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/src/hf_ipi.c b/src/hf_ipi.c
index 86f18c1..0964c13 100644
--- a/src/hf_ipi.c
+++ b/src/hf_ipi.c
@@ -8,9 +8,8 @@
 
 #include "hf/hf_ipi.h"
 
-#include "hf/arch/plat/ffa/notifications.h"
-
 #include "hf/cpu.h"
+#include "hf/ffa/notifications.h"
 #include "hf/plat/interrupts.h"
 
 /** Interrupt priority for Inter-Processor Interrupt. */