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/P2020RDB-PC_NAND_defconfig b/configs/P2020RDB-PC_NAND_defconfig
index af522d3..ff7bfd7 100644
--- a/configs/P2020RDB-PC_NAND_defconfig
+++ b/configs/P2020RDB-PC_NAND_defconfig
@@ -43,6 +43,7 @@
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_FSL_ESDHC=y
 CONFIG_MTD_NOR_FLASH=y
+CONFIG_MTD_PARTITIONS=y
 CONFIG_NAND=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_SPANSION=y