x86, amd: Use compute unit information to determine thread siblings

This information is vital for different load balancing policies.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
LKML-Reference: <20100930124156.GF20545@loge.amd.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>