drm/gem: Get rid of *_with_mnt helpers

drm/gem: Get rid of *_with_mnt helpers

drm_gem_object_init_with_mnt() and drm_gem_shmem_create_with_mnt() can
be removed now that the drivers use the new drm_gem_huge_mnt_create()
and drm_gem_get_huge_mnt() helpers.

v5:
- use drm_gem_has_huge_mnt() helper
- compile out shmem_file_setup_with_mnt() call in builds with
  CONFIG_TRANSPARENT_HUGEPAGE=n

v9:
- replace drm_gem_has_huge_mnt() with drm_gem_get_huge_mnt()

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Link: https://patch.msgid.link/20251205182231.194072-8-loic.molinari@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>