Convert CONFIG_MTD_PARTITIONS et al to Kconfig

This converts the following to Kconfig:
   CONFIG_MTD_PARTITIONS
   CONFIG_MTD_DEVICE

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/cm_fx6_defconfig b/configs/cm_fx6_defconfig
index f10903e..d532719 100644
--- a/configs/cm_fx6_defconfig
+++ b/configs/cm_fx6_defconfig
@@ -51,6 +51,7 @@
 CONFIG_DM_KEYBOARD=y
 CONFIG_DM_MMC=y
 CONFIG_FSL_ESDHC=y
+CONFIG_MTD_PARTITIONS=y
 CONFIG_NAND=y
 CONFIG_NAND_MXS=y
 CONFIG_SPI_FLASH=y