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/10m50_defconfig b/configs/10m50_defconfig
index c79c9f6..acd7fb8 100644
--- a/configs/10m50_defconfig
+++ b/configs/10m50_defconfig
@@ -24,6 +24,7 @@
 CONFIG_ALTERA_SYSID=y
 CONFIG_MTD=y
 CONFIG_MTD_NOR_FLASH=y
+CONFIG_MTD_DEVICE=y
 CONFIG_ALTERA_QSPI=y
 CONFIG_PHY_MARVELL=y
 CONFIG_DM_ETH=y