powerpc/p2041: add RCW file for P2041RDB

All the dev boards of Freescale's QorIQ family have a RCW that is
supported by the u-boot.pbl build target. This patch adds one for the
P2041 dev board.

This RCW is suitable for the RAMBOOT_PBL scenarios and was tested on the
P2041RDB booting from the eSPI NOR Flash (P2041RDB_SPIFLASH config).

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>