benchmarks/hpl: let’s choose among various BLAS × MPI implementations

• Add a license
• Add options to choose MPI and BLAS implementations.
• Do not bump PORTREVISION because the default remains Netlib (excepted static vs shared libs).
• And also this fixes the port with BLAS 3.12

Caveat: may install an unneeded liblapack.

PR: 274882, 275860
Approved by: maintainer’s time-out