mx51 enchance the sd/mmc HW timing compatibility on mx51 boards.

Some cards have the CRC errors in read on mx51 BBG board.
Configure the eSDHC pad configurations to level up the
compatibility to fix this issue.
Signed-off-by: Richard Zhu <Hong-Xing.Zhu@freescale.com>
Tested-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>