KVM: x86/xen: Explicitly pad struct compat_vcpu_info to 64 bytes

Add a 2 byte pad to struct compat_vcpu_info so that the sum size of its
fields is actually 64 bytes.  The effective size without the padding is
also 64 bytes due to the compiler aligning evtchn_pending_sel to a 4-byte
boundary, but depending on compiler alignment is subtle and unnecessary.

Opportunistically replace spaces with tables in the other fields.

Cc: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210210182609.435200-6-seanjc@google.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>