ENGR00174155: i.mx6sdl: add 32bit DDR support on ARM2 board

The 32bit DDR script got from the following link:
http://compass.freescale.net/livelink/livelink/225194568/


MX6DL_init_DDR3_400MHZ_32bit_1.0.inc.txt?func=doc.Fetch&nodeid=225194568

The DDR hw connection on the ARM2 board is 64bit wire, but we can make it use
as 32bit, the side effect is that DDR access size will reduce to the half

Signed-off-by: Jason Liu <r64343@freescale.com>