feat(ras): move wait logic from assembley to C

SDEI test uses a flag to be updated through SDEI handler to ensure that
test has passed, this logic was implemented in assembly, move this logic
in C to make it easily readable.

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I4c92aa7a6fbeb5fcdb4c67b0166627a539609f18
diff --git a/tftf/tests/misc_tests/test_single_fault.c b/tftf/tests/misc_tests/test_single_fault.c
index dd30572..cacd0a7 100644
--- a/tftf/tests/misc_tests/test_single_fault.c
+++ b/tftf/tests/misc_tests/test_single_fault.c
@@ -11,7 +11,7 @@
 
 #ifdef __aarch64__
 
-uint64_t sdei_event_received;
+static volatile uint64_t sdei_event_received;
 extern void inject_unrecoverable_ras_error(void);
 extern int serror_sdei_event_handler(int ev, uint64_t arg);
 
@@ -51,6 +51,11 @@
 
 	inject_unrecoverable_ras_error();
 
+	/* Wait until the SError fires */
+	do {
+		dmbish();
+	} while (sdei_event_received == 0);
+
 	return TEST_RESULT_SUCCESS;
 }