Revert "imx: mx6: ddr correct tRFC and tXS"

This reverts commit 059323fb6a8f21637bb617919715c2427f24777c.

This commit 059323fb6a8f21637bb617919715c2427f24777c use JESD79-3E which
is not the newest spec. Should use JESD79-3F in which tRFC is 260ns for
4Gb chip.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Tim Harvey <tharvey@gateworks.com>
1 file changed