Convert CONFIG_ENV_IS_IN_FLASH to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_IS_IN_FLASH

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/calimain_defconfig b/configs/calimain_defconfig
index 48422dd..7476383 100644
--- a/configs/calimain_defconfig
+++ b/configs/calimain_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_DAVINCI=y
 CONFIG_TARGET_CALIMAIN=y
+CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_BOOTDELAY=0
 CONFIG_VERSION_VARIABLE=y
 # CONFIG_DISPLAY_CPUINFO is not set