Re-enable RF233 enable pin

[alevy]

In the current revision, the RF233 enable pin is tied to ground because of an original misdiagnosis of #7. Since that's now fixed we should re-establish the SAM4L's control over the RF233's enable pin.

• Test that controlling the enable pin from the SAM4L no longer browns out the SAM4L

• If it works, remove the trace/resistor grounding the enable pin.

[alevy]

In my experiments with an older board --- one without RF233_EN tied to ground, but with the power-related patch wires --- this still does not work. I believe @shaneleonard thinks this is related to the problem in #12 and the same fix might apply.

[shaneleonard]

Closing as this issue is now tracked by #14