drm/gma500: Rewrite GTT page insert/remove without struct gtt_range

struct gtt_range represents a GEM object and should not be used for GTT
setup. Change psb_gtt_insert() and psb_gtt_remove() to receive all
necessary parameters from their caller. This also eliminates possible
failure from psb_gtt_insert().

There's one exception in psb_gtt_restore(), which requires an upcast
from struct resource to struct gtt_range when restoring the GTT after
hibernation. A possible solution would track the GEM objects that need
restoration separately from the GTT resource.

Rename the functions to psb_gtt_insert_pages() and psb_gtt_remove_pages()
to reflect their similarity to MMU interfaces.

v3:
	* restore the comments about locking rules (Patrik)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211015084053.13708-10-tzimmermann@suse.de