ARM: Enable selection of SMP operations at boot time

Add a new 'smp_init' hook to machine_desc so platforms can specify a
function to be used to setup smp ops instead of having a statically
defined value.  The hook must return true when smp_ops are initialized.
If false the static mdesc->smp_ops will be used by default.

Add the definition of "bool" by including the linux/types.h file to
asm/mach/arch.h and make it self-contained.

Signed-off-by: Jon Medhurst <tixy@linaro.org>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>