ddr cfg: DRAM_RESET needs 0x00020030

The old value of 0x000e0030 will cause ethernet
timeout issues on the sabrelite and possibly other
boards using the KSZ9021.
I have no explanation as to why.

But this is a correct change, the TRM will be updated
to show that 00b is the only valid setting for bits
19-18 of DRAM_RESET.

My thanks go to Liu Hui(Jason) for this information.

Acked-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Stefano Babic <sbabic@denx.de>
Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>