LU-14904 ldiskfs: add support for Ubuntu20 kernel 5.4.0.80

LU-14904 ldiskfs: add support for Ubuntu20 kernel 5.4.0.80

Changes from newer 5.4.0 kernel version have been backported to
Ubuntu20. Test for Ubuntu 5.4.0.80 kernels so we use the correct
series file with the updated ext-simple-blockalloc.patch.

Test-Parameters: trivial
Change-Id: I73ad558a306ec50fb1ba45e6ab2c59aaec047197
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/44703
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>