drm/amdgpu: move gfx ecc functions to generic gfx file

gfx ras ecc common functions could be reused among all gfx generations

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>