drm/amdgpu: Fix GFX hang on SteamDeck when amdgpu is reloaded

drm/amdgpu: Fix GFX hang on SteamDeck when amdgpu is reloaded

When trying to unload amdgpu in the SteamDeck (TTY mode), the following
set of errors happens and the system gets unstable:

[..]
 [drm] Initialized amdgpu 3.64.0 for 0000:04:00.0 on minor 0
 amdgpu 0000:04:00.0: [drm:amdgpu_ib_ring_tests [amdgpu]] *ERROR* IB test failed on gfx_0.0.0 (-110).
 amdgpu 0000:04:00.0: amdgpu: ib ring test failed (-110).
[..]
 amdgpu 0000:04:00.0: amdgpu: SMU: I'm not done with your previous command: SMN_C2PMSG_66:0x0000001E SMN_C2PMSG_82:0x00000000
 amdgpu 0000:04:00.0: amdgpu: Failed to disable gfxoff!
 amdgpu 0000:04:00.0: amdgpu: SMU: I'm not done with your previous command: SMN_C2PMSG_66:0x0000001E SMN_C2PMSG_82:0x00000000
 amdgpu 0000:04:00.0: amdgpu: Failed to disable gfxoff!
[..]

When the driver initializes the GPU, the PSP validates all the firmware
loaded, and after that, it is not possible to load any other firmware
unless the device is reset. What is happening in the load/unload
situation is that PSP halts the GC engine because it suspects that
something is amiss. To address this issue, this commit ensures that the
GPU is reset (mode 2 reset) in the unload sequence.

Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rodrigo Siqueira <siqueira@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>