T4240/ramboot: enable PBL tool for T4240

Added a default RCW(1_28_6_12) and PBI configure file for T4240, so it can use
PBL tool to produce the ramboot image.

Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>