mx6sabresd: Make SPL DDR configuration to match the DCD table

mx6sabresd: Make SPL DDR configuration to match the DCD table

When using SPL on i.mx6 we frequently notice some DDR initialization
mismatches between the SPL code and the non-SPL code.

This causes stability issues like the ones reported at 7dbda25ecd6d7c
("mx6ul_14x14_evk: Pass refsel and refr fields to avoid hang") and also:
http://lists.denx.de/pipermail/u-boot/2016-September/266355.html .

As the non-SPL code have been tested for long time and proves to be reliable,
let's configure the DDR in the exact same way as the non-SPL case.

The idea is simple: just use the DCD table and write directly to the DDR
registers.

Retrieved the DCD tables from:
board/freescale/mx6sabresd/mx6q_4x_mt41j128.cfg
and
board/freescale/mx6sabresd/mx6qp.cfg
(NXP U-Boot branch imx_v2015.04_4.1.15_1.0.0_ga)

This method makes it easier for people converting from non-SPL to SPL code.

Other benefit is that the SPL binary size is reduced from 44 kB to 39.9 kB.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>