[test] Ensure SHA3 is idle before using KMAC

In some situations software seems to work fast enough that it can try to
use KMAC before SHA3 is idle after the previous use. Our testutils check
for this condition but error out rather than try to recover from it.

This change uses a very small timeout since it should become idle very
quickly ideally.

Signed-off-by: James Wainwright <james.wainwright@lowrisc.org>

Author: jwnrt

sw/device/tests/entropy_src_fw_override_test.c

@@ -262,6 +262,15 @@ static status_t entropy_config(
   return OK_STATUS();
 }
 
+/**
+ * Check whether KMAC's SHA3 state is idle.
+ */
+static bool kmac_is_idle(void) {
+  dif_kmac_status_t status;
+  CHECK_DIF_OK(dif_kmac_get_status(&kmac, &status));
+  return status.sha3_state == kDifKmacSha3StateIdle;
+}
+
 /**
  * Configure the entropy source in extract and insert mode and run some entropy
  * consumers.
@@ -328,6 +337,7 @@ status_t firmware_override_extract_insert(
   uint32_t output[8];
   LOG_INFO("Running KMAC...");
   for (int i = 0; i < kKmacRepeats; i++) {
+    IBEX_SPIN_FOR(kmac_is_idle(), 20);
     TRY(kmac_testutils_kmac(&kmac, kDifKmacModeKmacLen128, &software_key,
                             /*custom_string=*/NULL, /*custom_string_len=*/0,
                             /*message=*/"hello", /*message_len=*/6,