[PATCH] Remove arch/powerpc/boot/zImage file.

The bootwrapper Makefile does not clean up the 'zImage' file that
may be left laying around.  This patch removes it when cleaning that
directory.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>