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/gwventana_emmc_defconfig b/configs/gwventana_emmc_defconfig
index dbb9fba..4394842 100644
--- a/configs/gwventana_emmc_defconfig
+++ b/configs/gwventana_emmc_defconfig
@@ -58,6 +58,7 @@
 CONFIG_DWC_AHSATA=y
 CONFIG_SUPPORT_EMMC_RPMB=y
 CONFIG_FSL_ESDHC=y
+CONFIG_MTD_DEVICE=y
 CONFIG_PHYLIB=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y