systemd: add target python to depends

* pythonnative adds only python-native to DEPENDS, but we need target python for working python-config
checking for python-config... /OE/jansa-test/shr-core/tmp-eglibc/sysroots/x86_64-linux/usr/bin/python-native/python-config
Traceback (most recent call last):
  File "/OE/jansa-test/shr-core/tmp-eglibc/sysroots/x86_64-linux/usr/bin/python-native/python-config", line 24, in <module>
    pyver = sysconfig.get_config_var('VERSION')
  File "/OE/jansa-test/shr-core/tmp-eglibc/sysroots/x86_64-linux/usr/lib/python2.7/distutils/sysconfig.py", line 602, in get_config_var
    return get_config_vars().get(name)
  File "/OE/jansa-test/shr-core/tmp-eglibc/sysroots/x86_64-linux/usr/lib/python2.7/distutils/sysconfig.py", line 518, in get_config_vars
    func()
  File "/OE/jansa-test/shr-core/tmp-eglibc/sysroots/x86_64-linux/usr/lib/python2.7/distutils/sysconfig.py", line 416, in _init_posix
    raise DistutilsPlatformError(my_msg)
distutils.errors.DistutilsPlatformError: invalid Python installation: unable to open /OE/jansa-test/shr-core/tmp-eglibc/sysroots/om-gta02/usr/lib/python2.7/config/Makefile (No such file or directory)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>