Add common GFX RAS definitions.

v2: remove instance from amdgpu_gfx_ras_reg_entry,
    amdgpu_ras_err_status_reg_entry has already defined it.
v3: remove memory id definitions from amdgpu_gfx.h, they are
    related to IP version.
Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>