arm: socfpga: spl: Add support for booting from SD/MMC

Add code and configuration options to support booting from RAW
SD/MMC card as well as for ext4/vfat filesystems. Enable support
for booting from SD/MMC card, but don't enable the filesystem
support just yet to retain compatibility with old SoCFPGA card
format.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/configs/socfpga_arria5_defconfig b/configs/socfpga_arria5_defconfig
index 4ba4b8c..245d53c 100644
--- a/configs/socfpga_arria5_defconfig
+++ b/configs/socfpga_arria5_defconfig
@@ -7,3 +7,5 @@
 # CONFIG_CMD_FLASH is not set
 CONFIG_OF_CONTROL=y
 CONFIG_SPI_FLASH=y
+CONFIG_SPL_DM=y
+CONFIG_SPL_MMC_SUPPORT=y