ARM: AM43xx: Enable DDR dynamic IO power down for DDR3

This patch enables dynamically powering down the
IO receiver when not performing a read on DDR3 board.
This optimizes both active and standby power consumption.
This is derived from a patch that is done on AM335x[1]

[1] http://arago-project.org/git/projects/?p=u-boot-am33x.git;a=commit;h=6a9ee4bc72ece53fabf01825605fba3d71d5feb2Signed-off-by: NLokesh Vutla <lokeshvutla@ti.com>

board/ti/am43xx/board.c

@@ -188,7 +188,7 @@ const struct ctrl_ioregs ioregs_ddr3 = {
 	.dt1ioctl		= DDR3_DATA0_IOCTRL_VALUE,
 	.dt2ioctrl		= DDR3_DATA0_IOCTRL_VALUE,
 	.dt3ioctrl		= DDR3_DATA0_IOCTRL_VALUE,
-	.emif_sdram_config_ext	= 0x0043,
+	.emif_sdram_config_ext	= 0x0143,
 };
 
 const struct emif_regs ddr3_emif_regs_400Mhz = {