Move environment files from common/ to env/

About a quarter of the files in common/ relate to the environment. It
seems better to put these into their own subdirectory and remove the
prefix.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/Kconfig b/Kconfig
index 14740b4..c48f00e 100644
--- a/Kconfig
+++ b/Kconfig
@@ -380,6 +380,8 @@
 
 source "dts/Kconfig"
 
+source "env/Kconfig"
+
 source "net/Kconfig"
 
 source "drivers/Kconfig"