Documentation/x86: Switch to new Intel CPU model defines

New CPU #defines encode vendor and family as well as model
so "_FAM6" is no longer used in the #define names.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240611204814.353821-1-tony.luck@intel.com