buildroot

Makefile: add missing PHONY targets

Quite a few targets in the top-level Makefile were missing the .PHONY
marking. Now that the .PHONY declarations are next to the definition
of the targets, they are much easier to find.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>