feat(freertos): Simplify xtensa platform code

All normal ISRs are called by "_xt_isr_handler".

components/esp8266/include/rom/ets_sys.h

@@ -42,6 +42,7 @@ extern "C" {
 #define ETS_SOFT_INUM       7
 #define ETS_WDT_INUM        8
 #define ETS_FRC_TIMER1_INUM 9
+#define ETS_INT_MAX         14
 
 extern char NMIIrqIsOn;
 extern uint32_t WDEV_INTEREST_EVENT;