powerpc: vdso: Make vdso32 installation conditional in vdso_install

The 32-bit vDSO is not needed and not normally built for 64-bit
little-endian configurations.  However, the vdso_install target still
builds and installs it.  Add the same config condition as is normally
used for the build.

Fixes: e0d00591 ("powerpc/vdso: Disable building the 32-bit VDSO ...")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Makefile

@@ -409,7 +409,9 @@ vdso_install:
 ifdef CONFIG_PPC64
 	$(Q)$(MAKE) $(build)=arch/$(ARCH)/kernel/vdso64 $@
 endif
+ifdef CONFIG_VDSO32
 	$(Q)$(MAKE) $(build)=arch/$(ARCH)/kernel/vdso32 $@
+endif
 
 archclean:
 	$(Q)$(MAKE) $(clean)=$(boot)