x86, realmode: Make sure all generated files are listed in targets

Kbuild expects all generated files to be listed in the targets
variable.  If it isn't, weird things happen.

Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336595106-21135-1-git-send-email-jarkko.sakkinen@intel.com