ARM: dts: imx35-pdk: Fix memory region description

On imx35pdk there are two DRAM chip selects that are used:

CS0 at 0x80000000
CS1 at 0x90000000

Each bank is connected to 128MB of DRAM, giving a total of 256MB of system DRAM.

Fix the memory layout to describe the hardware appropriately.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>