Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/drm_agpsupport.c:61: warning: Function parameter or member 'dev' not described in 'drm_agp_info'
 drivers/gpu/drm/drm_agpsupport.c:61: warning: Function parameter or member 'info' not described in 'drm_agp_info'
 drivers/gpu/drm/drm_agpsupport.c:105: warning: Function parameter or member 'dev' not described in 'drm_agp_acquire'
 drivers/gpu/drm/drm_agpsupport.c:132: warning: Function parameter or member 'dev' not described in 'drm_agp_acquire_ioctl'
 drivers/gpu/drm/drm_agpsupport.c:132: warning: Function parameter or member 'data' not described in 'drm_agp_acquire_ioctl'
 drivers/gpu/drm/drm_agpsupport.c:132: warning: Function parameter or member 'file_priv' not described in 'drm_agp_acquire_ioctl'
 drivers/gpu/drm/drm_agpsupport.c:145: warning: Function parameter or member 'dev' not described in 'drm_agp_release'
 drivers/gpu/drm/drm_agpsupport.c:171: warning: Function parameter or member 'dev' not described in 'drm_agp_enable'
 drivers/gpu/drm/drm_agpsupport.c:171: warning: Function parameter or member 'mode' not described in 'drm_agp_enable'
 drivers/gpu/drm/drm_agpsupport.c:203: warning: Function parameter or member 'dev' not described in 'drm_agp_alloc'
 drivers/gpu/drm/drm_agpsupport.c:203: warning: Function parameter or member 'request' not described in 'drm_agp_alloc'
 drivers/gpu/drm/drm_agpsupport.c:256: warning: Function parameter or member 'dev' not described in 'drm_agp_lookup_entry'
 drivers/gpu/drm/drm_agpsupport.c:256: warning: Function parameter or member 'handle' not described in 'drm_agp_lookup_entry'
 drivers/gpu/drm/drm_agpsupport.c:279: warning: Function parameter or member 'dev' not described in 'drm_agp_unbind'
 drivers/gpu/drm/drm_agpsupport.c:279: warning: Function parameter or member 'request' not described in 'drm_agp_unbind'
 drivers/gpu/drm/drm_agpsupport.c:318: warning: Function parameter or member 'dev' not described in 'drm_agp_bind'
 drivers/gpu/drm/drm_agpsupport.c:318: warning: Function parameter or member 'request' not described in 'drm_agp_bind'
 drivers/gpu/drm/drm_agpsupport.c:363: warning: Function parameter or member 'dev' not described in 'drm_agp_free'
 drivers/gpu/drm/drm_agpsupport.c:363: warning: Function parameter or member 'request' not described in 'drm_agp_free'
 drivers/gpu/drm/drm_agpsupport.c:404: warning: Function parameter or member 'dev' not described in 'drm_agp_init'

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Faith <faith@valinux.com>
Cc: Gareth Hughes <gareth@valinux.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210115181601.3432599-24-lee.jones@linaro.org