package/pkg-meson.mk: set correct pkgconfig for native dependencies

This sets the correct build.pkg_config_path for all meson packages so
that dependencies with native: true will properly use the the host
pkgconfig instead of the target pkgconfig.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>