LPDDR2 script MX6SX_19x19_LPDDR2_JEDEC.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>
(Cherry pick from commit fac09919)