LU-15208 ldiskfs: add support for Ubuntu20 kernel 5.4.0.90

LU-15208 ldiskfs: add support for Ubuntu20 kernel 5.4.0.90

Also fix the lustre-build-ldiskfs.m4 to select correct series file.
We use -ge to check the kernel release version, so greater version
should come on top.

Change-Id: Id6b599ef5b2ea823e203aaa6a40917e49f98f4d9
Test-Parameters: trivial
Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-on: https://review.whamcloud.com/45547
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>