MLK-13551: mx6ull: evk: lpddr2: add pre charge command all

LPDDR2 script IMX6ULL_9X9_LPDDR2_400MHz_16bit_V1.2.inc

Updated to add precharge all command per JEDEC
The memory controller may optionally issue a precharge-all command
prior to the MRW reset command
This is strongly recommended to ensure robust DRAM initialization

Signed-off-by: Adrian Alonso <adrian.alonso@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>