[wlan][fcg-crypto] Move FCG and SAE codes into separate modules

The wlan-sae was recently renamed to wlan-cfg-crypto and now no longer
only holds just SAE code.

In this commit, the FiniteCyclicGroup trait is moved to a new module
`fcg`, and the SAE code is moved to a new module `sae`

Bug: 312485949
Test: CQ
Change-Id: Ice3be6ae1f5a277e362bf0e653aeb3d8e3790cd7
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1498338
Reviewed-by: Charles Celerier <chcl@google.com>
Commit-Queue: Kiet Tran <kiettran@google.com>
Fuchsia-Auto-Submit: Kiet Tran <kiettran@google.com>
12 files changed