tcg: add the CONFIG_TCG into Makefiles

Add the CONFIG_TCG for frontend and backend's files in the related
Makefiles.
Signed-off-by: NYang Zhong <yang.zhong@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Makefile.target

@@ -90,8 +90,8 @@ all: $(PROGS) stap
 # cpu emulator library
 obj-y += exec.o
 obj-y += accel/
-obj-y += tcg/tcg.o tcg/tcg-op.o tcg/optimize.o
-obj-y += tcg/tcg-common.o tcg/tcg-runtime.o
+obj-$(CONFIG_TCG) += tcg/tcg.o tcg/tcg-op.o tcg/optimize.o
+obj-$(CONFIG_TCG) += tcg/tcg-common.o tcg/tcg-runtime.o
 obj-$(CONFIG_TCG_INTERPRETER) += tcg/tci.o
 obj-$(CONFIG_TCG_INTERPRETER) += disas/tci.o
 obj-y += fpu/softfloat.o

accel/Makefile.objs

 obj-$(CONFIG_SOFTMMU) += accel.o
 obj-y += kvm/
-obj-y += tcg/
+obj-$(CONFIG_TCG) += tcg/
 obj-y += stubs/