gtk+-native: add gtk-update-icon-cache wrapper

gtk+-native: add gtk-update-icon-cache wrapper

This is needed in order to point where the pixbuf loaders.cache is
located and avoid warnings like the one below that appear when the
sstate is fetched from a remote machine:

(gtk-update-icon-cache:8913): GdkPixbuf-WARNING **: Cannot open pixbuf
loader module file '/REMOTE/MACHINE/PATH/loaders.cache': No such file or directory

(From OE-Core rev: 6665a41c6506039e6ba6cfdbaa941369e42d682f)

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>