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/ffa/hypervisor/cpu_cycles.c b/src/ffa/hypervisor/cpu_cycles.c
index ca76143..667e0e9 100644
--- a/src/ffa/hypervisor/cpu_cycles.c
+++ b/src/ffa/hypervisor/cpu_cycles.c
@@ -7,9 +7,9 @@
  */
 
 #include "hf/arch/other_world.h"
-#include "hf/arch/plat/ffa/indirect_messaging.h"
 
 #include "hf/api.h"
+#include "hf/ffa/indirect_messaging.h"
 #include "hf/vcpu.h"
 
 bool plat_ffa_run_forward(ffa_id_t vm_id, ffa_vcpu_index_t vcpu_idx,