Floss: LeRand controller plumbing

Add ability to call LeRand and provide a callback function.

Bug: 219982689
Test: mma -j $(nproc)
Test: ./build.py
Test: atest bluetooth_test_gd_unit --test-filter="*controller*"
Tag: #floss
Change-Id: Id501efa2073f3b8887f7ca9a3894050becebc5cd