feat(ulp): add support for ulp on esp32s31

components/ulp/test_apps/.build-test-rules.yml

@@ -4,6 +4,9 @@ components/ulp/test_apps/lp_core/lp_core_basic_tests:
   disable:
     - if: SOC_LP_CORE_SUPPORTED != 1
     - if: CONFIG_NAME == "xtal" and SOC_CLK_LP_FAST_SUPPORT_XTAL != 1
+    - if: IDF_TARGET in ["esp32s31"] and CONFIG_NAME == "xtal"
+      temporary: true
+      reason: CONFIG_RTC_FAST_CLK_SRC_XTAL not supported yet # TODO: [ESP32S31] IDF-15576
     - if: CONFIG_NAME == "lp_vad" and SOC_LP_VAD_SUPPORTED != 1
   depends_components:
     - ulp