When we reset the hub, the hub will actively drvie the PRTPWR signal of
the SITMRACE12 low, resulting in the SAM3 being shut off. If we want to
"survive" this, we need to set the OVERRIDE before we go into reset.
Right now, we never release the signal again, keeping ST12 enabled
permanently, which is of course not what we want in general.
You can compile the firmware for this new target using 'make
BOARD=qmod'.
The QMOD differs from simtrace+owhw in terms of low-level
initialization, as it has an external 12MHz clock at XIN, thus bypasses
the main oscillator and needs different PLL configuration.
