ARM: dts: sun8i: Add enable-method for SMP support for the A83T SoC

Add the use of enable-method property for SMP support which allows
to handle the SMP support for this specific SoC.

This commit adds enable-method properties to all CPU nodes.

Signed-off-by: Mylène Josserand <mylene.josserand@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>