drm/i915/gvt: emulate SKL_FUSE_STATUS and LCPLL_CTL for virtual monitor detection

Initialize the correct vreg for virtual monitor.
Set PG0/1/2 distribution and fuse download done in SKL_FUSE_STATUS.
Set PLL_ENABLE and PLL_LOCK in LCPLL_CTL.
Guest may need to check these registers for display monitor detection
on Skylake platforms.

Signed-off-by: Weinan Li <weinan.z.li@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>