platform/x86: intel_pmc_core: Add MPHY PLL clock gating status

ModPhy Common lanes can provide the clock gating status for the important
system PLLs such as Gen2 USB3PCIE2 PLL, DMIPCIE3 PLL, SATA PLL and MIPI
PLL.

On SPT, in addition to the crystal oscillator clock, the 100Mhz Gen2
USB3PCI2 PLL clock is used as the PLL reference clock and Gen2 PLL idling
is a necessary condition for the platform to go into low power states like
PC10 and S0ix.

Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@intel.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>