Core: Change the type of ns_caller from int32_t/uint32_t to bool

ns_caller is a function input parameter that is used to indicate
if the caller comes from non-secure. Change the type of it from
int32_t/uint32_t to bool so that it will be better to indicate
the meaning.

Change-Id: I5ae16de7a80fe426b05efed24882113e9c28d95f
Signed-off-by: Summer Qin <summer.qin@arm.com>
diff --git a/secure_fw/spm/spm_api_func.c b/secure_fw/spm/spm_api_func.c
index e22ff27..a0ad90e 100644
--- a/secure_fw/spm/spm_api_func.c
+++ b/secure_fw/spm/spm_api_func.c
@@ -73,7 +73,7 @@
             int32_t res;
 
             desc.args = args;
-            desc.ns_caller = 0U;
+            desc.ns_caller = false;
             desc.sfn = (sfn_t)part->static_data->partition_init;
             desc.sp_id = part->static_data->partition_id;
             res = tfm_core_sfn_request(&desc);