x86: implement missing x86_64 function smp_call_function_mask()

This patch defines the missing function smp_call_function_mask() for x86_64,
this is more or less a cut&paste of i386 function. It removes also some
duplicate code.

This function is needed by KVM to execute a function on some CPUs.

AK: Fixed description
AK: Moved WARN_ON(irqs_disabled) one level up to not warn in the panic case.
[ tglx: arch/x86 adaptation ]

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>