refactor: remove `stdnoreturn.h` includes

The `noreturn` macro and `_Noreturn` keywords are deprecated in C23. The
reccommended way to indicate noreturn is now `[[noreturn]]`, which uses
the new C23 attribute syntax.

Change-Id: Ib923fce8bbe97597aa5ed27bb0962a107191022b
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/test/hftest/device_psci.c b/test/hftest/device_psci.c
index b27338f..d146026 100644
--- a/test/hftest/device_psci.c
+++ b/test/hftest/device_psci.c
@@ -10,7 +10,7 @@
 
 #include "test/hftest.h"
 
-noreturn void hftest_device_reboot(void)
+[[noreturn]] void hftest_device_reboot(void)
 {
 	arch_reboot();
 }