kexec-tools: fix build failure on aarch64_be architecture

* refresh/cleanup the patch to apply cleanly on 2.0.9
* get rid of configure - it's autogenerated
* configure.ac: use aarch64* wildcard

Signed-off-by: Fathi Boudra <fathi.boudra@linaro.org>
Signed-off-by: Ross Burton <ross.burton@intel.com>