mx6ul_14x14_evk: don't use array for SD2 card detect pad

Only a single pad is changed to change sdhc2_dat3 from an
SDIO pin to and from GPIO4:5, so remove the array and use
the imx_iomux_v3_setup_pad() routine.

Signed-off-by: Eric Nelson <eric@nelint.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>