env: Migrate CONFIG_ENV_IS_IN_FAT options to Kconfig

We rename the various FAT_ENV_xxx options to CONFIG_ENV_FAT_xxx so that
they can be modified via Kconfig.  Migrate all existing users to the new
values.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/hikey_defconfig b/configs/hikey_defconfig
index 6df04de..be6ff3d 100644
--- a/configs/hikey_defconfig
+++ b/configs/hikey_defconfig
@@ -4,6 +4,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="hi6220-hikey"
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_ENV_IS_IN_FAT=y
+CONFIG_ENV_FAT_INTERFACE="mmc"
+CONFIG_ENV_FAT_DEVICE_AND_PART="1:1"
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_BOARD_EARLY_INIT_F=y
@@ -18,5 +20,4 @@
 CONFIG_USB=y
 CONFIG_USB_DWC2=y
 CONFIG_USB_STORAGE=y
-CONFIG_FAT_WRITE=y
 CONFIG_OF_LIBFDT_OVERLAY=y