drm/amdgpu: Fix the warning info when removing amdgpu device

Actually, the drm_dev_enter in psp_cmd_submit_buf does not
protect anything. If DRM device is unplugged, it will always
check the condition in WARN_ON. So drop drm_dev_enter and
drm_dev_exit in psp_cmd_submit_buf.

When removing amdgpu, the calling order is as follows:
amdgpu_pci_remove
    drm_dev_unplug
    amdgpu_driver_unload_kms
        amdgpu_device_fini_hw
            amdgpu_device_ip_fini_early
                psp_hw_fini
                    psp_ras_terminate
                        psp_ta_unloadye
                            psp_cmd_submit_buf

[ 4507.740388] Call Trace:
[ 4507.740389]  <TASK>
[ 4507.740391]  psp_ta_unload+0x44/0x70 [amdgpu]
[ 4507.740485]  psp_ras_terminate+0x4d/0x70 [amdgpu]
[ 4507.740575]  psp_hw_fini+0x28/0xa0 [amdgpu]
[ 4507.740662]  amdgpu_device_fini_hw+0x328/0x442 [amdgpu]
[ 4507.740791]  amdgpu_driver_unload_kms+0x51/0x60 [amdgpu]
[ 4507.740875]  amdgpu_pci_remove+0x5a/0x140 [amdgpu]
[ 4507.740962]  ? _raw_spin_unlock_irqrestore+0x27/0x43
[ 4507.740965]  ? __pm_runtime_resume+0x60/0x90
[ 4507.740968]  pci_device_remove+0x39/0xb0
[ 4507.740971]  device_remove+0x46/0x70
[ 4507.740972]  device_release_driver_internal+0xd1/0x160
[ 4507.740974]  driver_detach+0x4a/0x90
[ 4507.740975]  bus_remove_driver+0x6c/0xf0
[ 4507.740976]  driver_unregister+0x31/0x50
[ 4507.740977]  pci_unregister_driver+0x40/0x90
[ 4507.740978]  amdgpu_exit+0x15/0x120 [amdgpu]

v2: fix commit message style issue

Signed-off-by: lyndonli <Lyndon.Li@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>