Convert CONFIG_DOS_PARTITION to Kconfig

This converts the following to Kconfig:
   CONFIG_DOS_PARTITION

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/bcm7260_defconfig b/configs/bcm7260_defconfig
index 39a83fa..257d810 100644
--- a/configs/bcm7260_defconfig
+++ b/configs/bcm7260_defconfig
@@ -25,6 +25,7 @@
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_EXT4=y
 CONFIG_CMD_FS_GENERIC=y
+CONFIG_DOS_PARTITION=y
 CONFIG_OF_BOARD=y
 CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_MMC=y