Makefile: fix build when VPATH is outside GIT tree

Steve Ellcey / Leon Alrae reported that QEMU fails to build when
the VPATH directory is outside of the GIT tree, and the system
emulators & tools build is disabled. eg

   cd ..
   mkdir build
   cd build
   ../qemu/configure --disable-system --disable-tools
   make
   (...)
   make[1]: *** No rule to make target `../qom/object.o', needed by `qemu-aarch64'. Stop.
   make: *** [subdir-aarch64-linux-user] Error 2

The problem is due to the fact that some sub directory deps
were listed against SOFTMMU_SUBDIR_RULES instead of SUBDIR_RULES,
so were only processed for system emulators, not user emalutors.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
Message-Id: <1442570495-22029-1-git-send-email-berrange@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -176,7 +176,6 @@ SOFTMMU_SUBDIR_RULES=$(filter %-softmmu,$(SUBDIR_RULES))
 
 $(SOFTMMU_SUBDIR_RULES): $(block-obj-y)
 $(SOFTMMU_SUBDIR_RULES): $(crypto-obj-y)
-$(SOFTMMU_SUBDIR_RULES): $(qom-obj-y)
 $(SOFTMMU_SUBDIR_RULES): config-all-devices.mak
 
 subdir-%:
@@ -201,7 +200,7 @@ subdir-dtc:dtc/libfdt dtc/tests
 dtc/%:
 	mkdir -p $@
 
-$(SUBDIR_RULES): libqemuutil.a libqemustub.a $(common-obj-y)
+$(SUBDIR_RULES): libqemuutil.a libqemustub.a $(common-obj-y) $(qom-obj-y) $(crypto-aes-obj-$(CONFIG_USER_ONLY))
 
 ROMSUBDIR_RULES=$(patsubst %,romsubdir-%, $(ROMS))
 romsubdir-%: