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/da850_am18xxevm_defconfig b/configs/da850_am18xxevm_defconfig
index c76321f..9283bf9 100644
--- a/configs/da850_am18xxevm_defconfig
+++ b/configs/da850_am18xxevm_defconfig
@@ -37,6 +37,8 @@
 CONFIG_DM=y
 CONFIG_DM_I2C=y
 CONFIG_DM_I2C_COMPAT=y
+CONFIG_MTD_DEVICE=y
+CONFIG_MTD_PARTITIONS=y
 CONFIG_DM_SPI_FLASH=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y