package/dtc: needs host-pkgconf unconditionally

Commits 495e757d (package/dtc: add optional libyaml dependency) and
e43d9072 (package/dtc: fix build without libyaml), added a conditional
dependency to host-pkgconf, when libyaml is enabled, while commit
56d6dd45 (package/dtc: disable valgrind) explicitly disabled support of
valgrind.

However, presence of libyaml, as well as that of valgrind, *is* detected
by calling pkg-config:

    NO_VALGRIND := $(shell $(PKG_CONFIG) --exists valgrind; echo $$?)
    NO_YAML := $(shell $(PKG_CONFIG) --exists yaml-0.1; echo $$?)

Passing NO_YAML=1 or NO_VALGRIND=1 do not prevent the tests from being
executed, which would yield messages like:

    /bin/sh: 1: /home/ymorin/dev/buildroot/O/host/bin/pkg-config: not found

(note however that, even if the test is executed, the value we pass on
the command line still takes precedence, and the support for either is
properly disabled.)

So, move the dependency on host-pkgconfig out of the condition. Ditto
for the host package.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Cc: Titouan Christophe <titouan.christophe@railnova.eu>
Cc: Carlos Santos <unixmania@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>