drm/amdgpu: fix aperture iounmap skipped on device removal

drm/amdgpu: fix aperture iounmap skipped on device removal

amdgpu_pci_remove() calls drm_dev_unplug() before invoking the fini
routines. After drm_dev_unplug() the drm_dev_enter() guard in
amdgpu_ttm_fini() always returns false, so iounmap() for
aper_base_kaddr is silently skipped. On connected_to_cpu hardware
ioremap_cache() maps the aperture as WB; when iounmap() is skipped the
stale WB PAT entry persists. On reload IP discovery's
memremap(MEMREMAP_WC) on the same aperture range hits a WB/WC conflict,
producing an ioremap error and failing re-probe.

Remove the drm_dev_enter() guard and call iounmap() unconditionally.
The aperture mapping is plain MMIO and does not require device-presence
protection. Surprise-removal cleanup of aper_base_kaddr is already
handled unconditionally by amdgpu_device_unmap_mmio().

Fixes: 62d5f9f7110a ("drm/amdgpu: Unmap MMIO mappings when device is not unplugged")
Signed-off-by: Asad Kamal <asad.kamal@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>