KVM: rename vtd.c to iommu.c

Impact: file renamed

The code in the vtd.c file can be reused for other IOMMUs as well. So
rename it to make it clear that it handle more than VT-d.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index c023435..00f46c2 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -8,7 +8,7 @@
 common-objs += $(addprefix ../../../virt/kvm/, kvm_trace.o)
 endif
 ifeq ($(CONFIG_DMAR),y)
-common-objs += $(addprefix ../../../virt/kvm/, vtd.o)
+common-objs += $(addprefix ../../../virt/kvm/, iommu.o)
 endif
 
 EXTRA_CFLAGS += -Ivirt/kvm -Iarch/x86/kvm