Update maximum kernel version to 5.4

Increase the maximum supported kernel version to 5.4.  This was
verified using the Fedora 5.4.2-300.fc31.x86_64 kernel.

Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #9754
Closes #9759

META

@@ -6,5 +6,5 @@ Release:       1
 Release-Tags:  relext
 License:       CDDL
 Author:        OpenZFS on Linux
-Linux-Maximum: 5.3
+Linux-Maximum: 5.4
 Linux-Minimum: 2.6.32