[mc1322x] Sleep testing.

[Mariano Alvira]

Hello everyone,

I've finished super-rough code for sleeping (see sleep.c in
mc1322x-tests). There was a nice gotcha in that you must turn off the
radio before sleeping, otherwise the 1322 resets itself when it wakes
up. Other than that it wasn't too difficult.

This part has two sleep modes, hibernate and doze.

Hibernate does not keep the main oscillator running and so uses less
power than doze, however, if you want a precise timebase you must also
have an external 32 kHz crystal. You can use the internal "2kHz" ring
oscillator but the actual frequency of that thing is from 1kHz-4kHz.

Doze uses the reference oscillator (24MHz) and so uses more power
compared to hibernate, but doesn't require the 32 kHz crystal for
precise timing.