See the top level README for information on where to find the
schematic and programmers reference manual for the ARM processor
on the raspberry pi.  Also find information on how to load and run
these programs.

Based on uart02 and blinker05.  Like blinker05 this is a multi stage
program killing three birds with one stone.  First it uses polling
of the interrupt status lines to show what happens to the registers, etc
when an rx based interrupt occurs.  Then it uses interrupt polling to
receive characters rather than the uart status register.  Then it
enables the interrupts to the arm and uses an interrupt service routine
to receive characters from the uart.

As with other parts of this mini uart, the documentation has errors,
bits that are marked as not used were required to make this work.  When
working with this mini uart also have as a reference a real 16550 manual
if it doesnt work the way the BCM manual says, then pretend it is a
real 16550 and see what happens.

Note that the mini uart interrupt is not interrupt 57 uart_int, it is
interrupt 29 aux_int.