OMAP4430/60: EMIF: errata: Prohibit usage of Power-Down mode

A ZQ calibration long command is issued every time on exit
from active power-down and precharge power-down modes
when EMIF is configured to use Power-down mode
(EMIF_PWR_MGMT_CTRL.REG_LP_MODE=0x4).

Due to very short periods of power-down cycles, ZQ calibration
overhead creates bandwidth issues and increases overall system
power consumption.

As result, the guideline is to not allow Power-down mode and,
therefore, to not have set the
EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field to 0x4.

TI Errata i743; IMPACTED: OMAP4430/60 all revisions

Change-Id: Ib82f28e6e0c6c046ea277b90a78dc82c1ee82417
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Vitaly Chernooky <vitaly.chernooky@ti.com>