x86: Centaur Isaiah processor to use sysenter in 64-bit compatibility mode rather than syscall

Upcoming 64 bit processors from Centaur can use sysenter.

Signed-off-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Jesse Ahrens <jahrens@centtech.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>