We need to maintain backwards compatibility with device trees that don't
define an enable method. At the same time we want the device tree to be
able to specify an enable-method and have it stick.

Previously by having smp assigned in the DT_MACHINE definition this
would be picked up by setup_arch() and override whatever
arm_dt_init_cpu_maps() had configured. Now we move the initial
assignment of default smp_ops to a dt_fixup and let
arm_dt_init_cpu_maps() override that if the device tree defines an
enable-method.

[olof@lixom.net: Wrap set_smp_ops() in CONFIG_SMP.]
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Tested-by: Gregory CLEMENT <gregory.clement@bootlin.com> (on AX3)
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>