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/socfpga_de0_nano_soc_defconfig b/configs/socfpga_de0_nano_soc_defconfig
index 643542d..d56cb7d 100644
--- a/configs/socfpga_de0_nano_soc_defconfig
+++ b/configs/socfpga_de0_nano_soc_defconfig
@@ -48,6 +48,7 @@
 CONFIG_SYS_I2C_DW=y
 CONFIG_DM_MMC=y
 CONFIG_MMC_DW=y
+CONFIG_MTD_DEVICE=y
 CONFIG_PHY_MICREL=y
 CONFIG_PHY_MICREL_KSZ90X1=y
 CONFIG_DM_ETH=y