kconfig: warn about leading whitespace for menu prompts

Kconfig does its own indentation of menu prompts, so warn about and ignore
leading whitespace.  Remove also a few unnecessary newlines after other
warning prints.

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>