ISR: check for address in IRAM

[d-a-v]

closes #5780
closes #5779

[dok-net]

Refer to the ESP32 sources' FunctionalInterrupt.cpp:
void IRAM_ATTR interruptFunctional(void* arg)

But ESP8266 FunctionalInterrupt.cpp is missing this patch:

--- a/cores/esp8266/FunctionalInterrupt.cpp
+++ b/cores/esp8266/FunctionalInterrupt.cpp
@@ -11,7 +11,7 @@ typedef void (voidFuncPtrArg)(void);
extern "C" void ICACHE_RAM_ATTR __attachInterruptArg(uint8_t pin, voidFuncPtr userFunc, void*fp , int mode);

-void interruptFunctional(void* arg)
+void ICACHE_RAM_ATTR interruptFunctional(void* arg)
{
ArgStructure* localArg = (ArgStructure*)arg;
if (localArg->functionInfo->reqScheduledFunction)

Which leaves the commited IRAM check (ab12516) firing all the time:
ISR not in IRAM!

I'm converting EspSoftwareSerial to use FunctionInterrupt in order to save the ISR table.
The PR for this is #6002.