drm/amdgpu/swsmu: drop smu i2c bus on navi1x

Stop registering the SMU i2c bus on navi1x.  This leads to instability
issues when userspace processes mess with the bus and also seems to
cause display stability issues in some cases.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1314
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1341


Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>