Config.in files: whitespace cleanup

This patch fixes the following whitespace problems in Config.in files:
- trailing whitespace
- spaces instead of tabs for indentation
- help text not indented with tab + 2 spaces

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>