drm/i915: Move PCH_NOP to -1

So we can later use PCH >= comparisons. The ultimate goal
is to make it easier for us to introduce a new platform
with south display engine on PCH just by reusing the previous
one.
Suggested-by: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190308214300.25057-2-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -524,6 +524,7 @@ struct i915_psr {
 };
 
 enum intel_pch {
+	PCH_NOP = -1,	/* PCH without south display */
 	PCH_NONE = 0,	/* No PCH present */
 	PCH_IBX,	/* Ibexpeak PCH */
 	PCH_CPT,	/* Cougarpoint/Pantherpoint PCH */
@@ -532,7 +533,6 @@ enum intel_pch {
 	PCH_KBP,        /* Kaby Lake PCH */
 	PCH_CNP,        /* Cannon Lake PCH */
 	PCH_ICP,	/* Ice Lake PCH */
-	PCH_NOP,	/* PCH without south display */
 };
 
 enum intel_sbi_destination {