Transceiver52M: Downsample receive path to 1 sample-per-symbol

We don't need to run the full 4 sps receive signal through the
GSM receiver. In fact, we're better off bandlimiting the signal
(because of noise) and downsampling (for efficiency). Run both
through the quarter rate polyphase resampler.

In the absence of interference (external or internal generated)
this allows decoding below -100 dBm on most devices with a
signal generator reference signal.

Signed-off-by: Thomas Tsou <tom@tsou.cc>
Transceiver52M: Update device offset timings

Update empirically determined device Tx/Rx offset settings
for new modulator configuration. These offsets are the
combinations of filter group delays and other device lag
times that occur before and after the sample timing point
in the FPGA.

Signed-off-by: Thomas Tsou <tom@tsou.cc>