board: venice: fix dram bus config for GW7902/GW7903/GW7904

board: venice: fix dram bus config for GW7902/GW7903/GW7904

The GW7902/GW7903/GW7904 have an alternate databus layout affecting a few
of the DDRC and DDR PHY registers.

The 512MB configuration used this alternate bus layout. Change
the 512MB config to the standard bus configuration and add a generic
function to patch the DDRC/PHY configs for the alternate bus layout.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>