fstests: update sparse file & negative timestamp tests for exfat

exfat cannot do sparse files or negative timestamps, so exclude
tests which require these.

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

common/rc

@@ -2357,7 +2357,7 @@ _require_fs_space()
 _require_sparse_files()
 {
     case $FSTYP in
-    hfsplus)
+    hfsplus|exfat)
         _notrun "Sparse files not supported by this filesystem type: $FSTYP"
 	;;
     *)
@@ -4188,9 +4188,10 @@ _check_xfs_scrub_does_unicode() {
 	return 0
 }
 
+# exfat timestamps start at 1980 and cannot be prior to epoch
 _require_negative_timestamps() {
 	case "$FSTYP" in
-	ceph)
+	ceph|exfat)
 		_notrun "$FSTYP does not support negative timestamps"
 		;;
 	esac