Convert CONFIG_ENV_IS_IN_SPI_FLASH et al to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_IS_IN_SPI_FLASH
   CONFIG_ENV_IS_NOWHERE
   CONFIG_ENV_OFFSET
   CONFIG_ENV_OVERWRITE
   CONFIG_ENV_SECT_SIZE
   CONFIG_SYS_MMC_ENV_DEV
   CONFIG_SYS_MMC_ENV_PART

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/octeontx2_96xx_defconfig b/configs/octeontx2_96xx_defconfig
index 4ab2395..011bc79 100644
--- a/configs/octeontx2_96xx_defconfig
+++ b/configs/octeontx2_96xx_defconfig
@@ -64,6 +64,7 @@
 CONFIG_EFI_PARTITION=y
 CONFIG_PARTITION_TYPE_GUID=y
 CONFIG_OF_BOARD=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_USE_ENV_SPI_BUS=y
 CONFIG_ENV_SPI_BUS=0