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/arch/arm/mach-integrator/Kconfig b/arch/arm/mach-integrator/Kconfig
index d506ee5..5146e51 100644
--- a/arch/arm/mach-integrator/Kconfig
+++ b/arch/arm/mach-integrator/Kconfig
@@ -11,11 +11,13 @@
 config ARCH_INTEGRATOR_CP
 	bool "Support Integrator/CP platform"
 	select ARCH_CINTEGRATOR
+	imply ENV_IS_IN_FLASH
 
 endchoice
 
 config ARCH_CINTEGRATOR
 	bool
+	imply ENV_IS_IN_FLASH
 
 choice
 	prompt "Integrator core module select"