ARM: renesas: Scrub duplicate memory nodes from DT on Gen3

Scrub duplicate /memory@* node entries here. Some R-Car DTs might
contain multiple /memory@* nodes, however fdt_fixup_memory_banks()
either generates single /memory node or updates the first /memory
node. Any remaining memory nodes are thus potential duplicates.

However, it is not possible to delete all the memory nodes right
away, since some of those might not be DRAM memory nodes, but some
sort of other memory. Thus, delete only the memory nodes which are
in the R-Car3 DBSC ranges.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>