python-smartpm: add gettext-native to DEPENDS

python-smartpm: add gettext-native to DEPENDS

Fixes the following failure at do_install building python-smartpm-native
if gettext-native has not already been built and gettext tools are not
installed on the host:

| compiling locale/it/LC_MESSAGES/smart.po -> locale/it/LC_MESSAGES/smart.mo
| sh: msgfmt: command not found
...
| creating $D/usr/share/share/locale/it/LC_MESSAGES
| error: can't copy 'locale/it/LC_MESSAGES/smart.mo': doesn't exist or not a regular file

Note that we need gettext-native in DEPENDS and not "inherit gettext"
here because for native variants, gettext.bbclass instead adds
gettext-minimal-native to DEPENDS and that does not provide the msgfmt
command.

(From OE-Core rev: e8d903e2d5e0c0df18dfd9561c3f8ef340297f1f)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>