Amdgpu and nouveau call vga_switcheroo_process_delayed_switch() from
their lastclose callbacks. Call it from drm_lastclose(), so that the
driver functions can finally be removed. Only PCI devices with enabled
switcheroo do the delayed switching. The call has no effect on other
hardware.

v2:
- move change to drm_lastclose() (Sima)
- update docs for vga_switcheroo_process_delayed_switch()

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240812083000.337744-2-tzimmermann@suse.de