Add the support of AARCH32 in endian head file. The code is also
imported from FreeBSD 11.0. It's based on commit in below.

commit 4e3a5b4
Author: mmel <mmel@FreeBSD.org>
Date:   Tue Nov 10 12:02:41 2015 +0000

    ARM: Remove trailing whitespace from sys/arm/include
    No functional changes.

    Approved by:    kib (mentor)

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>