mxc: Fix SDHC multi-instance clock

On mxc, each SDHC instance has a dedicated clock, so gd->sdhc_clk is not
suitable for the multi-instance use case (initialization made directly with
fsl_esdhc_initialize()).

This patch fixes this issue by adding a configuration field for the SDHC input
clock frequency.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Eric Bénard <eric@eukrea.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Jason Liu <r64343@freescale.com>
Cc: Matt Sealey <matt@genesi-usa.com>
Cc: Andy Fleming <afleming@gmail.com>
diff --git a/board/esg/ima3-mx53/ima3-mx53.c b/board/esg/ima3-mx53/ima3-mx53.c
index e947330..41d6bb6 100644
--- a/board/esg/ima3-mx53/ima3-mx53.c
+++ b/board/esg/ima3-mx53/ima3-mx53.c
@@ -217,6 +217,7 @@
 		PAD_CTL_HYS_ENABLE | PAD_CTL_DRV_HIGH | PAD_CTL_PUE_PULL |
 		PAD_CTL_PKE_ENABLE | PAD_CTL_HYS_ENABLE | PAD_CTL_47K_PU);
 
+	esdhc_cfg.sdhc_clk = mxc_get_clock(MXC_ESDHC_CLK);
 	return fsl_esdhc_initialize(bis, &esdhc_cfg);
 }
 #endif