Avoid repetitive code in our C demos

[sy2002]

We might want to add

// convenient mechanism to access QNICE's Memory Mapped IO registers
#define MMIO( __x ) *((unsigned int volatile *) __x )

to c/qnice/monitor-lib/include/qmon.h as this is something that we need "all the time". Of course - if we do that - we need to sift through demos and remove this definition there.

Also common things that we need in our demos like non-blocking waiting for a key, as Michael did it in world.c:

      if (MMIO(IO_UART_SRA) & 1)
      {
         unsigned int tmp = MMIO(IO_UART_RHRA);
         break;
      }
      if (MMIO(IO_KBD_STATE) & KBD_NEW_ANY)
      {
         unsigned int tmp = MMIO(IO_KBD_DATA);
         break;
      }

We might want to add this to the .h file mentioned above and the implementation to c/qnice/monitor-lib/src/qmon.c

I bet there are a handful more things that we would find which would overall make our C demo code less redundant.

As this is just a "cleanup before a release" task, the priority is rather low, I guess :-)

I assigned it to myself and @MJoergen .

Obviously also some "how to program MMIO" and "how to program realtime" best practices need to be written around this.