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: 62d5f9f ("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>
(cherry picked from commit fb3f68a)
Cc: stable@vger.kernel.org

Author: Asad Kamal

drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c

@@ -2259,8 +2259,6 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
  */
 void amdgpu_ttm_fini(struct amdgpu_device *adev)
 {
-	int idx;
-
 	if (!adev->mman.initialized)
 		return;
 
@@ -2283,13 +2281,9 @@ void amdgpu_ttm_fini(struct amdgpu_device *adev)
 	amdgpu_ttm_unmark_vram_reserved(adev, AMDGPU_RESV_FW_VRAM_USAGE);
 	amdgpu_ttm_unmark_vram_reserved(adev, AMDGPU_RESV_DRV_VRAM_USAGE);
 
-	if (drm_dev_enter(adev_to_drm(adev), &idx)) {
-
-		if (adev->mman.aper_base_kaddr)
-			iounmap(adev->mman.aper_base_kaddr);
+	if (adev->mman.aper_base_kaddr) {
+		iounmap(adev->mman.aper_base_kaddr);
 		adev->mman.aper_base_kaddr = NULL;
-
-		drm_dev_exit(idx);
 	}
 
 	if (!adev->gmc.is_app_apu)