drm/i915: remove in_dbg_master check from intel_fbc.c

From our maintainer Daniel Vetter a few days ago:
  "Oh dear this is dead code. kdbg uses the fbcon, which always uses
  untiled, which means fbc will never be enabled. Also we have 0 users
  and 0 test coverage for kdbg on top of i915 (Jesse implemented it
  for fun years back). Imo just remove all this code."

Adding to what Daniel said: for kgdboc's KMS support,
intel_pipe_set_base_atomic() already manually disables FBC, so we
won't do the in_dbg_master() check there. This is essentially a revert
of:

commit c924b934
Author: Jason Wessel <jason.wessel@windriver.com>
Date:   Thu Aug 5 09:22:32 2010 -0500
    i915: when kgdb is active display compression should be off

Besides, it is not clear what is the exact problem caused by FBC, and
why other features such as PSR, DRRS, IPS and RPM are not also
checking for in_dbg_master(). IMHO we should either remove the code as
suggested by Daniel or we add some nice comments explaining why is FBC
so special.

v2: Rebase due to new patch order.

Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1446664257-32012-13-git-send-email-paulo.r.zanoni@intel.comSigned-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/intel_fbc.c

@@ -889,12 +889,6 @@ static void __intel_fbc_update(struct drm_i915_private *dev_priv)
 		goto out_disable;
 	}
 
-	/* If the kernel debugger is active, always disable compression */
-	if (in_dbg_master()) {
-		set_no_fbc_reason(dev_priv, "Kernel debugger is active");
-		goto out_disable;
-	}
-
 	/* WaFbcExceedCdClockThreshold:hsw,bdw */
 	if ((IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv)) &&
 	    ilk_pipe_pixel_rate(crtc->config) >=