Add support for cargo build of LMP

This change adds an option to skip generating Bluetooth packets using
bluetooth_packetgen if these were already built in advance.
It also adds crate definition for liblmp, similar to bt_packets.

Bug: 238726856
Tag: #floss
Test: cargo build
Ignore-AOSP-First: Cherry-picked from AOSP
Merged-In: Ib099b56c0eb39c37cb459132ddf2a813cb63ebf6
Change-Id: Ib099b56c0eb39c37cb459132ddf2a813cb63ebf6