x86/AMD: expose HWCR.TscFreqSel to guests

x86/AMD: expose HWCR.TscFreqSel to guests

Linux has been warning ("firmware bug") about this bit being clear for a
long time. While writable in older hardware it has been readonly on more
than just most recent hardware. For simplicitly report it always set (if
anything we may want to log the issue ourselves if it turns out to be
clear on older hardware) on CPU families 10h and up (in family 0fh the
bit is part of a larger field of different purpose).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Ian Jackson <iwj@xenproject.org>