target-i386: Rename cpuid.c

Name it cpu.c to align with other QOM'ified targets.
Signed-off-by: NAndreas Färber <afaerber@suse.de>

Makefile.target

@@ -87,7 +87,7 @@ endif
 endif
 libobj-y += helper.o
 ifeq ($(TARGET_BASE_ARCH), i386)
-libobj-y += cpuid.o
+libobj-y += cpu.o
 endif
 libobj-$(TARGET_SPARC64) += vis_helper.o
 libobj-$(CONFIG_NEED_MMU) += mmu.o