uboot-imx

drivers/ddr/fsl_ddr: Make SR_IE configurable

SR_IE(Self-refresh interrupt enable) is needed for
Hardware Based Self-Refresh. Make it configurable and let
board code handle the rest.

Signed-off-by: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Reviewed-by: York Sun <yorksun@freescale.com>