dtc: Improve and better integrate dtc and libfdt Makefiles

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> This patch substantially revamps the dtc Makefiles, in particular
> better integrating the Makefile for dtc proper with the Makefiles
> imported from libfdt for libfdt and the shared testsuite.  Notable
> changes:
> 	- No recursive make calls.  Instead subsidiary Makefiles are
> included into the top-level Makefile so we get a complete dependency
> information.
> 	- Common pattern rules, CFLAGS etc. shared between dtc, libfdt
> and testsuite, rather than separate copies.
> 	- Vaguely Kbuild-like non-verbose mode used by default, which
> makes warnings more prominent.
> 	- libfdt Makefile consists only of variable definitions and
> helper rules, to make it more easily embeddable into other Makefile
> systems.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

I like.

Applied.

Thanks!
jdl