Resolve L2SS-1010 "Antenna cables"

Closes L2SS-1010

tangostationcontrol/tangostationcontrol/common/__init__.py

+def subband_frequency(subband: int, clock: float, nyquist_zone: int) -> int:
+    """ Obtain the frequencies of a subband, given a clock and an antenna type. """
+    subband_width = clock / 1024
+    return (512 * nyquist_zone + subband) * subband_width