wrap MRAA lib's Gpio::isr() for IRQ support

[2bndy5]

I also removed MRAA exclusion from examples build. Previously, interruptConfigure.cpp was not built for MRAA driver.

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[2bndy5]

This seems to work on my RPi3 if example_linux/interruptConfigure.cpp does not call pinMode(IRQ_PIN, INPUT). If pinMode(IRQ_PIN, INPUT) is called, I get

terminate called after throwing an instance of 'GPIOException'
  what():  [GPIO::open] Could not set the pin direction; Invalid resource
Aborted

[2bndy5]

stranger and stranger.

with this example patch

diff --git a/examples_linux/interruptConfigure.cpp b/examples_linux/interruptConfigure.cpp
index ec71b7a..378b79f 100644
--- a/examples_linux/interruptConfigure.cpp
+++ b/examples_linux/interruptConfigure.cpp
@@ -119,8 +119,10 @@ int main(int argc, char** argv)
     // radio.printDetails();       // (smaller) function that prints raw register values
     // radio.printPrettyDetails(); // (larger) function that prints human readable data
 
+#ifndef MRAA
     // setup the digital input pin connected to the nRF24L01's IRQ pin
-    pinMode(IRQ_PIN, INPUT);
+    pinMode(IRQ_PIN, INPUT); // not needed for MRAA driver (causes error in most cases)
+#endif
 
     // register the interrupt request (IRQ) to call our
     // Interrupt Service Routine (ISR) callback function interruptHandler()

I get the following prompts:

brendan@rpi3-64bit:~/github/RF24/examples_linux/build $ ./interruptConfigure 
terminate called after throwing an instance of 'GPIOException'
  what():  [GPIO::open] Could not set the pin direction; Invalid resource
Aborted
brendan@rpi3-64bit:~/github/RF24/examples_linux/build $ ./interruptConfigure 
./interruptConfigure
Which radio is this? Enter '0' or '1'. Defaults to '0' 
terminate called after throwing an instance of 'IRQException'
  what():  [attachInterrupt] Could not set the pin as an input; Invalid resource
Aborted
brendan@rpi3-64bit:~/github/RF24/examples_linux/build $ ./interruptConfigure 
./interruptConfigure
Which radio is this? Enter '0' or '1'. Defaults to '0' 
*** PRESS 'T' to begin transmitting to the other node
*** PRESS 'R' to begin receiving from the other node
*** PRESS 'Q' to exit

and yet the example still works when it finally initializes the hardware as expected.

[2bndy5]

When I leave the pinMode() call in (for MRAA driver), it still works. It seems the MRAA lib is just having trouble initializing the hardware some how. 🤷🏼‍♂️ I should note that the TX role of the interrupt example is noticeably slower using MRAA, compared to any other driver. And this only works on my RPi3, MRAA doesn't seem to support the RPi4 very well.

[TMRh20]

This tests OK on my RPi model B with all tested examples with no error msgs.

[2bndy5]

I'm not happy with the performance, but it's better than no interrupt support using mraa driver.

The hardware unit problem is still perplexing though.