moxie: Remove ELF_MACHINE from cpu.h

moxie: Remove ELF_MACHINE from cpu.h

The bootloader can just pass EM_MOXIE directly, as that is architecture
specific code.

This removes another architecture specific definition from the global
namespace.

Cc: Anthony Green <green@moxielogic.com>
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>