drm/i810: drop device_is_agp callback

Use the same trick we used for i915 when we still had ums support:
Just initialize the agp support unconditionally in the driver load
function.

Unfortunately that means we need to export drm_agp_init again, but I
think that's a lesser evil.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170125062657.19270-9-daniel.vetter@ffwll.ch

drivers/gpu/drm/i810/i810_drv.h

@@ -124,7 +124,6 @@ extern int i810_driver_load(struct drm_device *, unsigned long flags);
 extern void i810_driver_lastclose(struct drm_device *dev);
 extern void i810_driver_preclose(struct drm_device *dev,
 				 struct drm_file *file_priv);
-extern int i810_driver_device_is_agp(struct drm_device *dev);
 
 extern long i810_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 extern const struct drm_ioctl_desc i810_ioctls[];