ARM: dts: bcm283x: Add 32-bit enable method for SMP

This patch adds the missing 32-bit enable method for SMP on BCM2836 and
BCM2837. The BCM2837 already has an enabled method, but this one only
works for 64-bit.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Tested-by: Eric Anholt <eric@anholt.net>