SSP: need clock driver for on-demand activation of MCLK/BCLK/LRCLK

[plbossart]

This is the mirror of the SOF issue https://github.com/thesofproject/sof/issues/629

We need the ability to activate audio clocks independently either at boot or on-demand. This will require a dedicated kernel module registering the clocks with the clock framework (as done in the Skylake driver) as well as a new IPC.