crypto: vmx - various build fixes

First up, clean up the generated .S files properly on a 'make clean'.
Secondly, force re-generation of these files when building for different
endian-ness than what was built previously. Finally, generate the new
files in the build tree, rather than the source tree.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/vmx/Makefile

@@ -10,10 +10,12 @@ endif
 quiet_cmd_perl = PERL $@
       cmd_perl = $(PERL) $(<) $(TARGET) > $(@)
 
-$(src)/aesp8-ppc.S: $(src)/aesp8-ppc.pl
-	$(call cmd,perl)
-  
-$(src)/ghashp8-ppc.S: $(src)/ghashp8-ppc.pl
-	$(call cmd,perl)
+targets += aesp8-ppc.S ghashp8-ppc.S
 
-.PRECIOUS: $(obj)/aesp8-ppc.S $(obj)/ghashp8-ppc.S
+$(obj)/aesp8-ppc.S: $(src)/aesp8-ppc.pl FORCE
+	$(call if_changed,perl)
+  
+$(obj)/ghashp8-ppc.S: $(src)/ghashp8-ppc.pl FORCE
+	$(call if_changed,perl)
+
+clean-files := aesp8-ppc.S ghashp8-ppc.S