ib62x0: Perform base CONFIG_DM enablement

As these boards support CONFIG_OF_CONTROL today, perform a basic
CONFIG_DM migration.

Cc: Luka Perkov <luka@openwrt.org>
Signed-off-by: NTom Rini <trini@konsulko.com>

configs/ib62x0_defconfig

@@ -9,6 +9,7 @@ CONFIG_ENV_SIZE=0x20000
 CONFIG_ENV_OFFSET=0xE0000
 CONFIG_DEFAULT_DEVICE_TREE="kirkwood-ib62x0"
 CONFIG_IDENT_STRING=" RaidSonic ICY BOX IB-NAS62x0"
+# CONFIG_SYS_MALLOC_F is not set
 CONFIG_BOOTDELAY=3
 CONFIG_USE_PREBOOT=y
 # CONFIG_DISPLAY_BOARDINFO is not set
@@ -35,6 +36,7 @@ CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_NETCONSOLE=y
+CONFIG_DM=y
 # CONFIG_MMC is not set
 CONFIG_MTD=y
 CONFIG_MTD_RAW_NAND=y