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/flea3_defconfig b/configs/flea3_defconfig
index 6bb83a0..f116b45 100644
--- a/configs/flea3_defconfig
+++ b/configs/flea3_defconfig
@@ -23,6 +23,7 @@
 CONFIG_MXC_GPIO=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
+CONFIG_MTD_PARTITIONS=y
 CONFIG_NAND=y
 CONFIG_NAND_MXC=y
 CONFIG_PHYLIB=y