powerpc: dts: turris1x.dts: Add CPLD reboot node

CPLD firmware can reset board by writing value 0x01 at CPLD memory offset
0x0d. Define syscon-reboot node for this reset support.

Fixes: 54c15ec3

 ("powerpc: dts: Add DTS file for CZ.NIC Turris 1.x routers")
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220713134429.18748-1-pali@kernel.org