Fix warnings from clang-16

Running clang-16 on mbedtls reports warnings of type "-Wstrict-prototypes".
This patch fixes these warnings by adding void to functions with no
arguments. The generate_test_code.py is modified to insert void into test
functions with no arguments in *.function files.

Signed-off-by: Gowtham Suresh Kumar <gowtham.sureshkumar@arm.com>
diff --git a/programs/test/udp_proxy.c b/programs/test/udp_proxy.c
index cc0bf79..d31947a 100644
--- a/programs/test/udp_proxy.c
+++ b/programs/test/udp_proxy.c
@@ -645,7 +645,7 @@
     memcpy(&prev[prev_len++], delay, sizeof(packet));
 }
 
-int send_delayed()
+int send_delayed(void)
 {
     uint8_t offset;
     int ret;