drm/amd/display: fix double free issue during amdgpu module unload

commit 20b5a8f9 upstream.

Flexible endpoints use DIGs from available inflexible endpoints,
so only the encoders of inflexible links need to be freed.
Otherwise, a double free issue may occur when unloading the
amdgpu module.

[  279.190523] RIP: 0010:__slab_free+0x152/0x2f0
[  279.190577] Call Trace:
[  279.190580]  <TASK>
[  279.190582]  ? show_regs+0x69/0x80
[  279.190590]  ? die+0x3b/0x90
[  279.190595]  ? do_trap+0xc8/0xe0
[  279.190601]  ? do_error_trap+0x73/0xa0
[  279.190605]  ? __slab_free+0x152/0x2f0
[  279.190609]  ? exc_invalid_op+0x56/0x70
[  279.190616]  ? __slab_free+0x152/0x2f0
[  279.190642]  ? asm_exc_invalid_op+0x1f/0x30
[  279.190648]  ? dcn10_link_encoder_destroy+0x19/0x30 [amdgpu]
[  279.191096]  ? __slab_free+0x152/0x2f0
[  279.191102]  ? dcn10_link_encoder_destroy+0x19/0x30 [amdgpu]
[  279.191469]  kfree+0x260/0x2b0
[  279.191474]  dcn10_link_encoder_destroy+0x19/0x30 [amdgpu]
[  279.191821]  link_destroy+0xd7/0x130 [amdgpu]
[  279.192248]  dc_destruct+0x90/0x270 [amdgpu]
[  279.192666]  dc_destroy+0x19/0x40 [amdgpu]
[  279.193020]  amdgpu_dm_fini+0x16e/0x200 [amdgpu]
[  279.193432]  dm_hw_fini+0x26/0x40 [amdgpu]
[  279.193795]  amdgpu_device_fini_hw+0x24c/0x400 [amdgpu]
[  279.194108]  amdgpu_driver_unload_kms+0x4f/0x70 [amdgpu]
[  279.194436]  amdgpu_pci_remove+0x40/0x80 [amdgpu]
[  279.194632]  pci_device_remove+0x3a/0xa0
[  279.194638]  device_remove+0x40/0x70
[  279.194642]  device_release_driver_internal+0x1ad/0x210
[  279.194647]  driver_detach+0x4e/0xa0
[  279.194650]  bus_remove_driver+0x6f/0xf0
[  279.194653]  driver_unregister+0x33/0x60
[  279.194657]  pci_unregister_driver+0x44/0x90
[  279.194662]  amdgpu_exit+0x19/0x1f0 [amdgpu]
[  279.194939]  __do_sys_delete_module.isra.0+0x198/0x2f0
[  279.194946]  __x64_sys_delete_module+0x16/0x20
[  279.194950]  do_syscall_64+0x58/0x120
[  279.194954]  entry_SYSCALL_64_after_hwframe+0x6e/0x76
[  279.194980]  </TASK>

Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Tim Huang <tim.huang@amd.com>
Reviewed-by: Roman Li <roman.li@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>