drm/amdgpu: add atomfirmware helper function to query sram ecc caps

sram ecc capability could be get from firmware_capability field in firmwareinfo table

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