smdk5420: board: add functions to init dfu environment settings

This commit extends SMDK5420 board's file by adding functions:
- get_dfu_alt_system()
- get_dfu_alt_boot()

This allows setting the DFU environment by function set_dfu_alt_info()
from: board/samsung/common/misc.c

Signed-off-by: Inha Song <ideal.song@samsung.com>
Cc: Akshay Saraswat <akshay.s@samsung.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>

board/samsung/smdk5420/smdk5420.c

@@ -19,6 +19,7 @@
 #include <power/tps65090_pmic.h>
 #include <i2c.h>
 #include <lcd.h>
+#include <mmc.h>
 #include <parade.h>
 #include <spi.h>
 #include <usb.h>
@@ -111,3 +112,32 @@ int board_usb_init(int index, enum usb_init_type init)
 	return dwc3_uboot_init(&dwc3_device_data);
 }
 #endif
+#ifdef CONFIG_SET_DFU_ALT_INFO
+char *get_dfu_alt_system(char *interface, char *devstr)
+{
+	return getenv("dfu_alt_system");
+}
+
+char *get_dfu_alt_boot(char *interface, char *devstr)
+{
+	struct mmc *mmc;
+	char *alt_boot;
+	int dev_num;
+
+	dev_num = simple_strtoul(devstr, NULL, 10);
+
+	mmc = find_mmc_device(dev_num);
+	if (!mmc)
+		return NULL;
+
+	if (mmc_init(mmc))
+		return NULL;
+
+	if (IS_SD(mmc))
+		alt_boot = CONFIG_DFU_ALT_BOOT_SD;
+	else
+		alt_boot = CONFIG_DFU_ALT_BOOT_EMMC;
+
+	return alt_boot;
+}
+#endif