MIPS: ingenic: Hardcode mem size for qi,lb60 board

Old Device Tree for the qi,lb60 (aka. Ben Nanonote) did not have a
'memory' node. The kernel would then read the memory controller
registers to know how much RAM was available.

Since every other supported board has had a 'memory' node from the
beginning, we can just hardcode a RAM size of 32 MiB when running with
an old Device Tree without the 'memory' node.

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