Add and use 'localedir' variable

Add and use 'localedir' variable

This avoids the hardcoding of ${libdir}/locale which is all over the place,
and will facilitate use of ${exec_prefix}/lib/locale instead of
${libdir}/locale.

This doesn't actually change any output at this time. Verified this with
buildhistory against the packages produced from core-image-base.

(From OE-Core rev: b744f4cc2912334b8493a89525fd02af8e9b8edf)

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>