drm/i915/dpkgc: Add VRR condition for DPKGC Enablement

DPKGC can now be enabled with VRR enabled if Vmin = Vmax = Flipline
is met.

Bspec: 68986
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240711044905.3306882-1-suraj.kandpal@intel.com