Revert "drm/i915: Add heuristic to determine better way to adjust brightness"

This reverts commit 560a758d39.

The DPCD backlight commits regress a Thinkpad X1 Carbon 4th Gen and a
BXT-P (in CI). Enabling dynamic backlight boots to a black screen, and
enabling DPCD backlight leads to a black screen after suspend/resume.

References: http://mid.mail-archive.com/20170706135349.6tu3lz7uehazlnnn@boom
References: http://mid.mail-archive.com/20170627132326.f2q3yn4bh5flji4q@boom
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101619
Reported-by: David Weinehall <david.weinehall@linux.intel.com>
Fixes: 560a758d39 ("drm/i915: Add heuristic to determine better way to adjust brightness")
Cc: Jenny TC <jenny.tc@intel.com>
Cc: David Weinehall <david.weinehall@linux.intel.com>
Cc: Puthikorn Voravootivat <puthik@chromium.org>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f49a89a05f18e90871c2eeadcdcd783ac7961cdf.1500542254.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_params.h

@@ -53,7 +53,6 @@
 	func(int, edp_vswing); \
 	func(int, reset); \
 	func(unsigned int, inject_load_failure); \
-	func(int, enable_dpcd_backlight); \
 	/* leave bools at the end to not create holes */ \
 	func(bool, alpha_support); \
 	func(bool, enable_cmd_parser); \
@@ -67,6 +66,7 @@
 	func(bool, verbose_state_checks); \
 	func(bool, nuclear_pageflip); \
 	func(bool, enable_dp_mst); \
+	func(bool, enable_dpcd_backlight); \
 	func(bool, enable_gvt)
 
 #define MEMBER(T, member) T member