msdosfs manuals: Improve visibility and linking

+ add `(FAT)` to all descriptions to enable `apropos fat`
+ xref all msdosfs(4) utilities in base to msdosfs(4)
+ xref msdosfs(4) to all msdosfs(4) utilities
+ remove unrelated fsck_ffs(8) from fsck_msdos(8)

MFC after:	3 days
Reviewed by:	mhorne
Approved by:	mhorne (mentor)
Pull Request:	https://github.com/freebsd/freebsd-src/pull/1557

(cherry picked from commit 93f4377caba08e4a47fb9f1878bf609bd4181564)

sbin/fsck_msdosfs/fsck_msdosfs.8

@@ -121,9 +121,8 @@ to assume
 as the answer to all operator questions.
 .El
 .Sh SEE ALSO
-.Xr fsck 8 ,
-.Xr fsck_ffs 8 ,
-.Xr mount_msdosfs 8
+.Xr msdosfs 4 ,
+.Xr fsck 8
 .Sh HISTORY
 The
 .Nm

sbin/mount_msdosfs/mount_msdosfs.8

@@ -33,7 +33,7 @@
 .Os
 .Sh NAME
 .Nm mount_msdosfs
-.Nd mount an MS-DOS file system
+.Nd mount an MS-DOS (FAT) file system
 .Sh SYNOPSIS
 .Nm
 .Op Fl 9ls

sbin/newfs_msdos/newfs_msdos.8

@@ -244,6 +244,7 @@ Create a 30MB image file, with the FAT partition starting
 newfs_msdos -C 30M -@63s ./somefile
 .Ed
 .Sh SEE ALSO
+.Xr msdosfs 4 ,
 .Xr gpart 8 ,
 .Xr newfs 8
 .Sh HISTORY

share/man/man5/msdosfs.5

@@ -6,7 +6,7 @@
 .Os
 .Sh NAME
 .Nm msdosfs
-.Nd MS-DOS file system
+.Nd MS-DOS (FAT) file system
 .Sh SYNOPSIS
 .Cd "options MSDOSFS"
 .Sh DESCRIPTION
@@ -65,8 +65,10 @@ may also be used to extract this information.
 .Sh SEE ALSO
 .Xr mount 2 ,
 .Xr unmount 2 ,
+.Xr fsck_msdosfs 8 ,
 .Xr mount 8 ,
 .Xr mount_msdosfs 8 ,
+.Xr newfs_msdos 8 ,
 .Xr umount 8
 .Sh AUTHORS
 This manual page was written by