linux_user: elfload: Default ELF_MACHINE to ELF_ARCH
In most (but not all) cases, ELF_MACHINE and ELF_ARCH are safely the
same. Default ELF_MACHINE to ELF_ARCH. This makes defining ELF_MACHINE
optional for target-*/cpu.h when they are known to match.
Reviewed-by: Richard Henderson <rth@twiddle.net> Acked-By: Riku Voipio <riku.voipio@linaro.org> Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>