fadvise64_64 on xtensa passes advice as the second argument and so must
be handled similar to PPC.

This fixes glibc testsuite tests posix/tst-posix_fadvise and
posix/tst-posix_fadvise64.
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>