x86/cpuid: Handle leaf 0x4 in guest_cpuid()

x86/cpuid: Handle leaf 0x4 in guest_cpuid()

Leaf 0x4 is reserved by AMD.  For Intel, it is a multi-invocation leaf with
ecx enumerating different cache details.

Add a new union for it in struct cpuid_policy, collect it from hardware in
calculate_raw_policy(), audit it in recalculate_cpuid_policy() and update
guest_cpuid() and update_domain_cpuid_info() to properly insert/extract data.

A lot of the data here will need further auditing/refinement when better
topology support is introduced, but for now, this matches the existing
toolstack behaviour.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>