qemuwrapper: Don't use STAGING_BINDIR_CROSS directly

qemuwrapper: Don't use STAGING_BINDIR_CROSS directly

We need the files to be tracked by sstate so we need to jump through
some hoops to ensure this happens. The cross bindir directory
isn't staged automatically so we need to handle this outselves.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>