Add zfs_file_* interface, remove vnodes

Provide a common zfs_file_* interface which can be implemented on all 
platforms to perform normal file access from either the kernel module
or the libzpool library.

This allows all non-portable vnode_t usage in the common code to be 
replaced by the new portable zfs_file_t.  The associated vnode and
kobj compatibility functions, types, and macros have been removed
from the SPL.  Moving forward, vnodes should only be used in platform
specific code when provided by the native operating system.

Reviewed-by: Sean Eric Fagan <sef@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #9556

include/os/linux/zfs/sys/policy.h

@@ -51,7 +51,7 @@ int secpolicy_zfs(const cred_t *);
 void secpolicy_setid_clear(vattr_t *, cred_t *);
 int secpolicy_setid_setsticky_clear(struct inode *, vattr_t *,
     const vattr_t *, cred_t *);
-int secpolicy_xvattr(xvattr_t *, uid_t, cred_t *, vtype_t);
+int secpolicy_xvattr(xvattr_t *, uid_t, cred_t *, mode_t);
 int secpolicy_vnode_setattr(cred_t *, struct inode *, struct vattr *,
     const struct vattr *, int, int (void *, int, cred_t *), void *);
 int secpolicy_basic_link(const cred_t *);

include/os/linux/zfs/sys/zfs_vnops.h

@@ -32,6 +32,7 @@
 #include <sys/fcntl.h>
 #include <sys/pathname.h>
 #include <sys/zpl.h>
+#include <sys/zfs_file.h>
 
 #ifdef	__cplusplus
 extern "C" {