rtc kconfig clarification

Make drivers/rtc/Kconfig be clearer about what the various "interfaces"
actually mean, by showing path names.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>