drm/i915: Drop early VLV WA to fix Voltage not getting dropped to Vmin

Drop WA to fix Voltage not getting dropped to Vmin when Gfx is power
gated for latest VLV revision.

Workaround fixed in Latest VLV revision. Forcing Gfx clk up not needed,
and Requesting the min freq should bring bring the voltage Vnn.

v2: Drop WA for Latest VLV revision (Ville)

Signed-off-by: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[Jani: modified code comment, reformatted the commit message a bit.]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>