In the mean time I found I needed the following in my hardware_init():
/* Setup board clock source. */
g_xtal0ClkFreq = 8000000U;
g_xtalRtcClkFreq = 32768U;
The bus clock now properly returns the 60MHz value I was expecting.
But I am stilling having trouble with the PDB when I enable the DMA trigger of the PDB.