spl mxc nand: Set symmetric mode

Set the spl mxc nand driver for IP 1.1 in symmetric mode, like the mtd driver.
In this way, for both drivers, one input clock period of the NFC IP will produce
one R/W cycle.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Signed-off-by: Scott Wood <scottwood@freescale.com>