drm/amdgpu: upgrade amdgpu_discovery struct ip to ip_v4

version 4 supports 64bit ip base address

Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>