vfio: Move vfio group specific code into group.c

This prepares for compiling out vfio group after vfio device cdev is
added. No vfio_group decode code should be in vfio_main.c, and neither
device->group reference should be in vfio_main.c.

No functional change is intended.

Link: https://lore.kernel.org/r/20221201145535.589687-11-yi.l.liu@intel.comReviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: Yu He <yu.he@intel.com>
Tested-by: Lixiao Yang <lixiao.yang@intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/vfio/Makefile

@@ -4,6 +4,7 @@ vfio_virqfd-y := virqfd.o
 obj-$(CONFIG_VFIO) += vfio.o
 
 vfio-y += vfio_main.o \
+	  group.o \
 	  iova_bitmap.o
 vfio-$(CONFIG_IOMMUFD) += iommufd.o
 vfio-$(CONFIG_VFIO_CONTAINER) += container.o

drivers/vfio/vfio.h

@@ -6,6 +6,7 @@
 #ifndef __VFIO_VFIO_H__
 #define __VFIO_VFIO_H__
 
+#include <linux/file.h>
 #include <linux/device.h>
 #include <linux/cdev.h>
 #include <linux/module.h>
@@ -15,6 +16,15 @@ struct iommu_group;
 struct vfio_device;
 struct vfio_container;
 
+void vfio_device_put_registration(struct vfio_device *device);
+bool vfio_device_try_get_registration(struct vfio_device *device);
+int vfio_device_open(struct vfio_device *device,
+		     struct iommufd_ctx *iommufd, struct kvm *kvm);
+void vfio_device_close(struct vfio_device *device,
+		       struct iommufd_ctx *iommufd);
+
+extern const struct file_operations vfio_device_fops;
+
 enum vfio_group_type {
 	/*
 	 * Physical device with IOMMU backing.
@@ -66,6 +76,18 @@ struct vfio_group {
 	struct iommufd_ctx		*iommufd;
 };
 
+int vfio_device_set_group(struct vfio_device *device,
+			  enum vfio_group_type type);
+void vfio_device_remove_group(struct vfio_device *device);
+void vfio_device_group_register(struct vfio_device *device);
+void vfio_device_group_unregister(struct vfio_device *device);
+int vfio_device_group_use_iommu(struct vfio_device *device);
+void vfio_device_group_unuse_iommu(struct vfio_device *device);
+void vfio_device_group_close(struct vfio_device *device);
+bool vfio_device_has_container(struct vfio_device *device);
+int __init vfio_group_init(void);
+void vfio_group_cleanup(void);
+
 #if IS_ENABLED(CONFIG_VFIO_CONTAINER)
 /* events for the backend driver notify callback */
 enum vfio_iommu_notify_type {