x86/cpu: Drop unused X86_VENDOR_* values

x86/cpu: Drop unused X86_VENDOR_* values

Xen only has CPU drivers for Intel, Centaur and AMD.  All other contributions
to X86_VENDOR_NUM simply make the cpu_devs[] array longer, reducing the
efficiency of get_cpu_vendor()

There is one remaning hidden reference to X86_VENDOR_CYRIX in the MTRR code.
However, as far as I can tell, Cyrix never realeased a 64bit processor.  It is
therefore dead code.

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