x86: lfence fix

LFENCE is available on XMM2 or higher Intel CPUs - not XMM or higher...

this caused boot failures on XMM1 & !XMM1 capable CPUs.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>