build: move obj-TARGET-y variables to nested Makefile.objs

Also drop duplicate occurrence of device-hotplug.o.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/Makefile.objs

@@ -0,0 +1,13 @@
+obj-y += mc146818rtc.o pc.o
+obj-y += apic_common.o apic.o kvmvapic.o
+obj-y += sga.o ioapic_common.o ioapic.o piix_pci.o
+obj-y += vmport.o
+obj-y += pci-hotplug.o smbios.o wdt_ib700.o
+obj-y += debugcon.o multiboot.o
+obj-y += pc_piix.o
+obj-y += pc_sysfw.o
+obj-$(CONFIG_XEN) += xen_platform.o xen_apic.o
+obj-$(CONFIG_KVM) += kvm/clock.o kvm/apic.o kvm/i8259.o kvm/ioapic.o kvm/i8254.o
+obj-$(CONFIG_SPICE) += qxl.o qxl-logger.o qxl-render.o
+
+obj-y := $(addprefix ../,$(obj-y))