meson: move libfdt together with other dependencies

Move the libfdt detection code together with other dependencies instead
of keeping it with subprojects.  This has the disadvantage of performing
the detection even if no target requires libfdt; but it has the advantage
that Kconfig will be able to observe the availability of the library.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed