[PATCH] x86_64: Provide ability to choose using shortcuts for IPI in flat mode.

This patch provides an option to switch broadcast or use mask version for
sending IPI's.  If CONFIG_HOTPLUG_CPU is defined, we choose not to use
broadcast shortcuts by default, otherwise we choose broadcast mode as default.

both cases, one can change this via startup cmd line option, to choose
no-broadcast mode.

	no_ipi_broadcast=1

This is provided on request from Andi Kleen, since he doesnt agree with
replacing IPI shortcuts as a solution for CPU hotplug.  Without removing
broadcast IPI's, it would mean lots of new code for __cpu_up() path, which
would acheive the same results.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Acked-by: Andi Kleen <ak@muc.de>
Acked-by: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>