s390/vdso32: add vdso32.lds to targets

This fixes a permanent rebuild of the 32 bit vdso. The RPM build process
was first calling 'make bzImage' and 'make modules' as a second step.
This caused a recompilation of vdso32.so, which in turn also changed
the build-id of vmlinux.

Fixes: 779df224

 ("s390/vdso: add minimal compat vdso")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>