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/porter_defconfig b/configs/porter_defconfig
index 17937aa..6efa641 100644
--- a/configs/porter_defconfig
+++ b/configs/porter_defconfig
@@ -61,6 +61,8 @@
 CONFIG_DM_MMC=y
 CONFIG_RENESAS_SDHI=y
 CONFIG_MTD=y
+CONFIG_MTD_DEVICE=y
+CONFIG_MTD_PARTITIONS=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_BAR=y
 CONFIG_SPI_FLASH_SPANSION=y