ARM: dts: BCM63xx: Add SMP nodes and required properties

Update bcm63138.dtsi with the following:

- enable-method for both CPU nodes
- brcm,bcm63138-bootlut node
- resets properties to point to the correct PMB controller to release
  the secondary CPU from reset

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>