drm: Inline AGP wrappers into their only callers

The AGP wrapper functions serve no purpose. They used to handle
builds that have CONFIG_AGP unset. But their callers are all in
drm_agpsupport.c, which only gets build with CONFIG_AGP.

v2:
	* clarify CONFIG_AGP in commit description (Daniel)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210112081035.6882-2-tzimmermann@suse.de