Linux 5.6 compat: time_t

As part of the Linux kernel's y2038 changes the time_t type has been
fully retired.  Callers are now required to use the time64_t type.

Rather than move to the new type, I've removed the few remaining
places where a time_t is used in the kernel code.  They've been
replaced with a uint64_t which is already how ZFS internally
handled these values.

Going forward we should work towards updating the remaining user
space time_t consumers to the 64-bit interfaces.

Reviewed-by: Matthew Macy <mmacy@freebsd.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #10052
Closes #10064

include/os/linux/spl/sys/time.h

@@ -85,7 +85,7 @@ gethrestime(inode_timespec_t *ts)
 #endif
 }
 
-static inline time_t
+static inline uint64_t
 gethrestime_sec(void)
 {
 #if defined(HAVE_INODE_TIMESPEC64_TIMES)

include/sys/vdev_impl.h

@@ -272,7 +272,7 @@ struct vdev {
 	range_tree_t	*vdev_initialize_tree;	/* valid while initializing */
 	uint64_t	vdev_initialize_bytes_est;
 	uint64_t	vdev_initialize_bytes_done;
-	time_t		vdev_initialize_action_time;	/* start and end time */
+	uint64_t	vdev_initialize_action_time;	/* start and end time */
 
 	/* TRIM related */
 	boolean_t	vdev_trim_exit_wanted;
@@ -293,7 +293,7 @@ struct vdev {
 	uint64_t	vdev_trim_rate;		/* requested rate (bytes/sec) */
 	uint64_t	vdev_trim_partial;	/* requested partial TRIM */
 	uint64_t	vdev_trim_secure;	/* requested secure TRIM */
-	time_t		vdev_trim_action_time;	/* start and end time */
+	uint64_t	vdev_trim_action_time;	/* start and end time */
 
 	/* for limiting outstanding I/Os (initialize and TRIM) */
 	kmutex_t	vdev_initialize_io_lock;