drm/amdgpu: add clearstate_defs.h

This header provides for format for the GCA blocks
clear state (i.e., default state).  Each GCA version
has a specific clear state.

Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Jammy Zhou <Jammy.Zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>