drm/amd/powerplay: avoid disabling ECC if RAS is enabled for VEGA20

Program THM_BACO_CNTL.SOC_DOMAIN_IDLE=1 will tell VBIOS to disable ECC when
BACO exit. This can save BACO exit time by PSP on none-ECC SKU. Drop the setting
for ECC supported SKU.

Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>