drm/amdgpu: correct umc poison mode set value

For GFX 11.0.3, Due to security policy, there is no way to check UcFatalEn
field of UMCCH0_0_GeccCtrl to identify UMC poison mode. This is workaround
force set umc poison mode as 1 for GFX 11.0.3

Signed-off-by: Stanley.Yang <Stanley.Yang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>