Versions of esdhc_send_cmd() in imx-esdhc.c and imx-esdhc-pbl.c
implement almost the same algorithm. To avoid code repetition, move
that code to imx-esdhc-common.c and adjust all of the users
accordingly.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>