Define it for i386 too.

This is a synthetic flag that signifies that the CPU's TSC runs
at a constant P state invariant frequency.

Fix up the logic on x86-64/i386 to set it on all known CPUs.
Use the AMD defined bit to set it on future AMD CPUs.

Cc: venkatesh.pallipadi@intel.com
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>