Fix recent pxa270 serial breakage This fixes a copy/paste bug introduced in commit 2d48377a8531de63ec1d0c4b9b1959dc4b78356c that pushed TARGET_WORDS_BIGENDIAN dependency to board level. Signed-off-by: Lars Munch <lars@segv.dk> Signed-off-by: Blue Swirl <blauwirbel@gmail.com>