x86: AMD core-pair topology detection code

x86: AMD core-pair topology detection code

This patch is to support core-pair topology introduced by AMD CPUs,
which introduces a new concept of [core, compute unit]. There is a new
feature bit for topology extension in CPUID:0x80000001. Also a new
CPUID 0x8000001E is introduced for CPU topology enumeration. This
patch collects the sibling information from the new CPUID and will be
stored in the sibling map in Xen hypervisor.

Signed-off-by: Wei Huang <wei.huang2@amd.com>