classes/recipes: remove unnecessary qemu inherit and use qemuwrapper-cross

classes/recipes: remove unnecessary qemu inherit and use qemuwrapper-cross

These classes/recipes inherit qemu.bbclass but do not use anything from it.
What they use is qemuwrapper-cross, which is needed at do_rootfs time and
needs to be pulled-in by PACKAGE_WRITE_DEPS.

Also, in meta/conf/layer.conf, exclude qemuwrapper-cross deps for all arch
recipes that depend on it. This it ensure allarch recipes have the same
signature across different machines.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>