mx6qsabreauto: Add SPL support

Add support for mx6q, mx6dl and mx6qp sabreauto boards in SPL.

Retrieved the mx6q DCD table from:
board/freescale/mx6qsabreauto/imximage.cfg

Retrieved the mx6dl DCD table from:
board/freescale/mx6qsabreauto/mx6dl.cfg

Retrieved the mx6qp DCD table from:
board/freescale/mx6qsabreauto/mx6qp.cfg

Flashed SPL and u-boot.img to an SD card and could successfully boot it
on mx6q, mx6qp and mx6dl sabreauto boards.

Signed-off-by: Vanessa Maegima <vanessa.maegima@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Stefano Babic <sbabic@denx.de>