arm: ls1021a: Add QSPI or IFC support in SD boot

As QSPI and IFC are pin-multiplexed on LS1021A, only IFC is supported in
SD boot now. For the customer's demand, QSPI needs to be supported in SD
boot too.

This patch adds QSPI or IFC support in SD boot according to the
corresponding defconfig. For detail, ls1021atwr_sdcard_ifc_defconfig is
used to support IFC in SD boot and ls1021atwr_sdcard_qspi_defconfig is
used to support QSPI in SD boot.

Signed-off-by: Alison Wang <alison.wang@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>