coreutils: enable xattrs by default for nativesdk

When using coreutils nativesdk (e.g. with buildtools-tarball) for
running oe-core builds, a number of recipes/classes/etc. expect xattr
support. This requirement is also expressed by the existing
PACKAGECONFIG_class-native default including xattrs.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>