x86/cpuid: Handle leaf 0x1 in guest_cpuid()

x86/cpuid: Handle leaf 0x1 in guest_cpuid()

The features words, ecx and edx, are already audited as part of the featureset
logic.  The existing leaf 0x80000001 dynamic logic has its SYSCALL adjustment
split out, as the rest of the adjustments are common with leaf 0x1.  The
existing leaf 0x1 feature adjustments from {pv,hvm}_cpuid() are moved
wholesale into guest_cpuid(), although deduped against the common adjustments.

The eax word is family/model/stepping information, and is fine to use as
provided by the toolstack, although with reserved bits cleared.

The ebx word is more problematic.  The low 8 bits are the brand ID and safe to
pass straight through.  The next 8 bits are the CLFLUSH line size.  This value
is forwarded straight from hardware, as nothing good can possibly come of
providing an alternative value to the guest.

The next 8 bits are slightly different between Intel and AMD, but are both
some property of the number of logical cores in the current physical package.
For now, the toolstack value is used unchanged until better topology support
is available.

The final 8 bits are the initial legacy APIC ID.  For HVM guests, this was
overridden to vcpu_id * 2.  The same logic is now applied to PV guests, so
guests don't observe a constant number on all vcpus via their emulated or
faulted view.

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