Move btif_dm and l2cap coc specific code in their own files.

This helps improve readability and cleanup excess responsibilities in btif_sock file.

Bug: 328310541
Test: m -j $(nproc)
Flag: EXEMPT ; simple moving of code inside the same layer (no thread jumps or anything of that sorts)
Change-Id: Id64db31d5d2ba17c6dbdde6c94a4cc3ebd1abe49