Extending FreeBSD UIO Struct

In FreeBSD the struct uio was just a typedef to uio_t. In order to
extend this struct, outside of the definition for the struct uio, the
struct uio has been embedded inside of a uio_t struct.

Also renamed all the uio_* interfaces to be zfs_uio_* to make it clear
this is a ZFS interface.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Closes #11438

include/sys/crypto/common.h

@@ -244,7 +244,7 @@ typedef struct crypto_data {
 		iovec_t cdu_raw;		/* Pointer and length	    */
 
 		/* uio scatter-gather format */
-		uio_t	*cdu_uio;
+		zfs_uio_t	*cdu_uio;
 
 	} cdu;	/* Crypto Data Union */
 } crypto_data_t;