apalis_imx6: fix broken fsl_esdhc_imx conversion

Commit e37ac717 ("Convert to use fsl_esdhc_imx for i.MX platforms")
converted FSL_ESDHC to FSL_ESDHC_IMX, but the config check for
apalis_imx6 wasn't updated accordantly.

Signed-off-by: Ricardo Salveti <ricardo@foundries.io>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Max Krummenacher <max.krummenacher@toradex.com>