powerpc: dts: Add DTS file for CZ.NIC Turris 1.x routers

CZ.NIC Turris 1.0 and 1.1 are open source routers, they have dual-core
PowerPC Freescale P2020 CPU and are based on Freescale P2020RDB-PC-A board.
Hardware design is fully open source, all firmware and hardware design
files are available at Turris project website:

https://docs.turris.cz/hw/turris-1x/turris-1x/
https://project.turris.cz/en/hardware.html

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220624085550.20570-1-pali@kernel.org