ARM: shmobile: kzm9g-reference dts: Declare the full 512 MiB of RAM

Traditionally, the first 16 MiB of RAM was reserved for the RT
processor.  However, this is incompatible with CONFIG_AUTO_ZRELADDR=y,
which requires that the start address of physical memory is a multiple
of 128 MiB.

As CONFIG_AUTO_ZRELADDR=y is enabled for multi-platform kernels, declare
RAM to start at 0x40000000.

While at it, reclaim the last 8 MiB of RAM, too, so the full 512 MiB is
available. Note that kzm9g_defconfig still has
CONFIG_MEMORY_START=0x41000000 and CONFIG_MEMORY_SIZE=0x1f000000, so
before the advent of DT we scribbled over the last 8 MiB, too.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>