SPM: Rename local handle pointer variable name

Rename the connection handle struct pointer name to
"handle" or "conn_handle" to indicate it is a handle
pointer.

The API "spm_get_handle_by_signal()" is used by IPC
backend only, fix the missing backend config macro of it.

Signed-off-by: Mingyang Sun <mingyang.sun@arm.com>
Change-Id: I705f6c4c63452d39d7bc142da90043b85a82854c
diff --git a/secure_fw/spm/include/ffm/backend.h b/secure_fw/spm/include/ffm/backend.h
index 7c3bce2..d5e470c 100644
--- a/secure_fw/spm/include/ffm/backend.h
+++ b/secure_fw/spm/include/ffm/backend.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  *
@@ -33,13 +33,13 @@
 
     /* Runtime model-specific message handling mechanism. */
     psa_status_t (*messaging)(struct service_t *p_serv,
-                              struct conn_handle_t *hdl);
+                              struct conn_handle_t *handle);
 
     /*
      * Runtime model-specific message replying.
      * Return the connection handle or the acked status code.
      */
-    psa_status_t (*replying)(struct conn_handle_t *hdl, int32_t status);
+    psa_status_t (*replying)(struct conn_handle_t *handle, int32_t status);
 };
 
 /* RUNTIME MODEL BACKENDS DECLARATION */