HV:treewide:rename struct pic and iommu_domain

For data structure types "struct pic and struct iommu_domain",
its name is identical with variable name in the same scope.
This MISRA C  violation is detected.

Naming convention rule:If the data structure type is used by only one
module and its name meaning is simplistic, its name needs prefix
shorten module name.
Naming convention rule:Variable name can be shortened from its
data structure type name.

The following udpates are made:
struct pic pic-->struct i8259_reg_state i8259
struct iommu_domain iommu_domain-->struct iommu_domain iommu

V1-->V2:
	Update "struct iommu_domain iommu_domain-->struct iommu_domain iommu"

Signed-off-by: Xiangyang Wu <xiangyang.wu@linux.intel.com>
Reviewed-by: Junjie Mao <junjie.mao@intel.com>

Author: Xiangyang Wu

hypervisor/arch/x86/guest/vm.c

@@ -268,9 +268,9 @@ int shutdown_vm(struct vm *vm)
 	/* TODO: De-initialize I/O Emulation */
 	free_io_emulation_resource(vm);
 
-	/* Free iommu_domain */
-	if (vm->iommu_domain != NULL) {
-		destroy_iommu_domain(vm->iommu_domain);
+	/* Free iommu */
+	if (vm->iommu != NULL) {
+		destroy_iommu_domain(vm->iommu);
 	}
 
 	bitmap_clear_lock(vm->attr.id, &vmid_bitmap);