drm/amd/display: Fix DM I2C teardown race

drm/amd/display: Fix DM I2C teardown race

DM I2C adapters can remain visible to userspace while DM teardown is
already in progress. A concurrent i2c-dev transfer may then enter
amdgpu_dm_i2c_xfer() after the backing DM state has been torn down,
leading to a NULL pointer dereference.

Create a devres group around the DM I2C adapter lifetime and release it
at the start of dm_hw_fini(), before HPD, IRQ, and DM state are torn
down. This removes the I2C adapters first and waits for in-flight users
to drain before the structures used by amdgpu_dm_i2c_xfer() disappear.

This fixes a teardown ordering race seen during device removal:

BUG: kernel NULL pointer dereference
RIP: amdgpu_dm_i2c_xfer+0x122/0x1c0 [amdgpu]
Call Trace:
__i2c_transfer
i2c_transfer
i2cdev_ioctl_rdwr

Fixes: 5b3eca05cfb0 ("drm/amd/display: Use devm_i2c_add_adapter to simplify i2c cleanup logic")
Signed-off-by: Geoffrey McRae <geoffrey.mcrae@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>