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_socrates_defconfig b/configs/socfpga_socrates_defconfig
index dcbab53..c5d5fa6 100644
--- a/configs/socfpga_socrates_defconfig
+++ b/configs/socfpga_socrates_defconfig
@@ -49,6 +49,7 @@
 CONFIG_SYS_I2C_DW=y
 CONFIG_DM_MMC=y
 CONFIG_MMC_DW=y
+CONFIG_MTD_DEVICE=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_BAR=y
 CONFIG_SPI_FLASH_MACRONIX=y