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_arria5_defconfig b/configs/socfpga_arria5_defconfig
index 41c9880..9b18d3e 100644
--- a/configs/socfpga_arria5_defconfig
+++ b/configs/socfpga_arria5_defconfig
@@ -48,6 +48,7 @@
 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_SPANSION=y