ARM: dts: rockchip: add memory node for rk3229-echo-v10

ARM: dts: rockchip: add memory node for rk3229-echo-v10

when using upstream u-boot load kernel, reserves memory from early
allocator will fail if memory node is not specified.

===============================
Starting kernel ...

[    0.000000] Booting Linux on physical CPU 0xf00
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Initializing cgroup subsys cpuacctdd
...
[    0.000000] earlycon: Early serial console at MMIO32 0x11030000 (options '')
[    0.000000] bootconsole [uart0] enabled
[    0.000000] cma: Failed to reserve 16 MiB
[    0.000000] Memory policy: Data cache writealloc

This patch fix it.

Change-Id: I6a3c6b1e210bbc9a5240503ab7bf5ddab89910ba
Signed-off-by: Frank Wang <frank.wang@rock-chips.com>