LU-17226 build: create config option for l_getsepol

LU-17226 build: create config option for l_getsepol

Add a configuration option for l_getsepol.
l_getsepol is build by default unless the --disable-l_getsepol
option is given to configure.
lustre.spec.in builds l_getsepol by default and has its
dependencies as build requirements.

The implicit configuration check for the dependency
openssl-devel is removed and replaced by a BuildRequires.

Lustre-change: https://review.whamcloud.com/52849
Lustre-commit: 2777adcabd1032ddb886f913fa04d82a292ab379

Test-Parameters: trivial
Signed-off-by: Gian-Carlo DeFazio <defazio1@llnl.gov>
Change-Id: If71a2a4a524047edbd2b31e6fac7a42f36a030bf
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/54162
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>