drm: define drm_compat_ioctl NULL on CONFIG_COMPAT=n and reduce #ifdefs

If we define drm_compat_ioctl NULL on CONFIG_COMPAT=n, we don't have to
check for the config everywhere.

Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1478014844-27454-1-git-send-email-jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index f022f43..74476f5 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2901,6 +2901,8 @@ __i915_printk(struct drm_i915_private *dev_priv, const char *level,
 #ifdef CONFIG_COMPAT
 extern long i915_compat_ioctl(struct file *filp, unsigned int cmd,
 			      unsigned long arg);
+#else
+#define i915_compat_ioctl NULL
 #endif
 extern const struct dev_pm_ops i915_pm_ops;