Add a function to return ELF e_flags and use it
to select the CPU model.

Signed-off-by: YunQiang Su <syq@debian.org>
[lv: split the patch and some cleanup in get_elf_eflags()]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180220173307.25125-3-laurent@vivier.eu>