TQM5200: use automatic fdt memory fixup

Call fdt_fixup_memory() on the boards TQM5200, TQM5200_B, TQM5200S,
TB5200 and TB5200_B to fixup the /memory node with the memory values
detected by U-Boot.

Signed-off-by: Martin Krause <martin.krause@tqs.de>