xen/x86: Always print processor information at boot

xen/x86: Always print processor information at boot

It is generally useful information, which isn't directly available in the
hypervisor console log.

To get an appropriate string in this_cpu->c_vendor, drop the notion of
gcv_host_late.  All relevent information is available even during early
detection, and even Linux (as the ancestor of this code) as dropped the
distinction.

A sample log now looks like:

  (XEN) Domain heap initialised
  (XEN) CPU Vendor: Intel, Family 6, Model 71, Stepping 1 (raw 00040671)
  (XEN) found SMP MP-table at 000fd6c0

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