drm/amdgpu: drop duplicated ecc check for vega10 (v5)

The same ECC check has been executed in amdgpu_ras_init for vega10,
prior to gmc_v9_0_late_init.

v2: drop all atombios helper callings
v3: use bit operation
v4: correct inline comment, remove parity check statement
v5: squash in build fix

Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>