drm/amdgpu: Fix S3 test issue

During S3 test, when system wake up and resume, ras interface
is already allocated. Move workaround before ras jumps to resume
step in gfx_v9_0_ecc_late_init, and make sure workaround applied
during resume. Also remove unused mmGB_EDC_MODE clearing.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>