boot/uboot: add host-python-pylibfdt dependency if needed

Until now, BR2_TARGET_UBOOT_NEEDS_PYLIBFDT was only bringing host-swig
as a dependency, because U-Boot was building its own pylibfdt, which
requires host-swig.

However, since commit
231d79c81e9a1f8c2ef14861374a40fcdc5e6b33 ("boot/uboot: set DTC path
when BR2_TARGET_UBOOT_NEEDS_DTC"), in which we tell U-Boot to use the
Buildroot built DTC, a consequence is that U-Boot no longer builds its
own pylibfdt: it expects the system to provided it. So now,
BR2_TARGET_UBOOT_NEEDS_PYLIBFDT really needs to bring
host-python-pylibfdt. The dependency on host-swig is no longer needed,
as what we need is host-python-pylibfdt, and it is an internal detail
of pylibfdt that it needs host-swig to build.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/4749556137
  https://gitlab.com/buildroot.org/buildroot/-/jobs/4749556224
  https://gitlab.com/buildroot.org/buildroot/-/jobs/4749556227
  https://gitlab.com/buildroot.org/buildroot/-/jobs/4749556229
  https://gitlab.com/buildroot.org/buildroot/-/jobs/4749556230

Signed-off-by: Christian Stewart <christian@aperture.us>
Tested-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit f788a8f527c038112671ff6fdc968823a54cf3aa)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/uboot/uboot.mk

@@ -217,7 +217,7 @@ UBOOT_DEPENDENCIES += host-python3 host-python-setuptools
 endif
 
 ifeq ($(BR2_TARGET_UBOOT_NEEDS_PYLIBFDT),y)
-UBOOT_DEPENDENCIES += host-swig
+UBOOT_DEPENDENCIES += host-python-pylibfdt
 endif
 
 ifeq ($(BR2_TARGET_UBOOT_NEEDS_PYELFTOOLS),y)