MIPS: ingenic: DTS: Add memory info of GCW Zero

Add memory info of the GCW Zero in its devicetree. The bootloader
generally provides this information, but since it is fixed to 512 MiB,
it doesn't hurt to have it in devicetree. It allows the kernel to boot
without any parameter passed as argument.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>