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/rpi_2_defconfig b/configs/rpi_2_defconfig
index a6f3cd7..e0bf3e1 100644
--- a/configs/rpi_2_defconfig
+++ b/configs/rpi_2_defconfig
@@ -4,6 +4,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="bcm2836-rpi-2-b"
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_OF_BOARD_SETUP=y
+CONFIG_ENV_FAT_INTERFACE="mmc"
+CONFIG_ENV_FAT_DEVICE_AND_PART="0:1"
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot> "