arm64: dts: Add syscon based reboot in DT for NS2

To reset NS2, we simply have to write '0' to BIT[1] at offset 0x90
of CRMU space.

The above can be easily achieved by writing 0xfffffffd at offset 0x90
using syscon-reboot driver. We don't need to have separate driver for
rebooting NS2.

This patch enables syscon-reboot driver for NS2 using DT.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>