boards: siemens: iot2050: Fix boot configuration

The common env bits now come via ti_armv7_common.env, include it.
Furthermore restore the board-specific boot targets and their ordering
that is now enforced k3-wide differently. Finally, enable
CONFIG_LEGACY_IMAGE_FORMAT explicitly which got lost while turning
FIT_SIGNATURE on by default for k3 devices.

Fixes: 53873974 ("include: armv7: Enable distroboot across all configs")
Fixes: 4ae1a247 ("env: Make common bootcmd across all k3 devices")
Fixes: 86fab110 ("Kconfig: Enable FIT_SIGNATURE if ARM64")
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
diff --git a/include/configs/iot2050.h b/include/configs/iot2050.h
index 2177e0d..4968722 100644
--- a/include/configs/iot2050.h
+++ b/include/configs/iot2050.h
@@ -15,6 +15,17 @@
 
 #include <configs/ti_armv7_common.h>
 
+/*
+ * This defines all MMC devices, even if the basic variant has no mmc1.
+ * The non-supported device will be removed from the boot targets during
+ * runtime, when that board was detected.
+ */
+#undef BOOT_TARGET_DEVICES
+#define BOOT_TARGET_DEVICES(func) \
+       func(MMC, mmc, 1) \
+       func(MMC, mmc, 0) \
+       BOOT_TARGET_USB(func)
+
 #ifdef CONFIG_ENV_WRITEABLE_LIST
 #define CFG_ENV_FLAGS_LIST_STATIC					\
 	"board_uuid:sw,board_name:sw,board_serial:sw,board_a5e:sw,"	\