refactor(ff-a): replace `plat_ffa_` prefix for public functions

Replace `plat_ffa_` prefix with `ffa_{file_name}_` prefix. Only do so
for public functions to avoid unnecessary churn (private functions are
renamed in the next commit).

Change-Id: I847c218f134a2519a45a3af1d6c4b953db9c1cbb
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 91aa1ce..f2a9251 100644
--- a/src/ffa/hypervisor/cpu_cycles.c
+++ b/src/ffa/hypervisor/cpu_cycles.c
@@ -127,8 +127,9 @@
 	return (struct ffa_value){.func = FFA_SUCCESS_32};
 }
 
-struct ffa_value plat_ffa_error_32(struct vcpu *current, struct vcpu **next,
-				   enum ffa_error error_code)
+struct ffa_value ffa_cpu_cycles_error_32(struct vcpu *current,
+					 struct vcpu **next,
+					 enum ffa_error error_code)
 {
 	(void)current;
 	(void)next;