tools/libxc: Restore CPUID/MSR data found in the migration stream

tools/libxc: Restore CPUID/MSR data found in the migration stream

With all other pieces in place, it is now safe to restore the CPUID and MSR
data in the migration stream, rather than discarding them and using the higher
level toolstacks compatibility logic.

While this is a small patch, it has large implications for migrated/resumed
domains.  Most obviously, the CPU family/model/stepping data,
cache/tlb/etc. will no longer change behind the guests back.

Another change is the interpretation of the Xend cpuid strings.  The 'k'
option is not a sensible thing to have ever supported, and 's' is how how the
stream will end up behaving.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>