zephyr: Port liblc3 to Zephyr as external module
zephyr: Port liblc3 to Zephyr as external module

Add Zephyr module definition so that the project can be used as Zephyr
external module.

Fixes: https://github.com/zephyrproject-rtos/liblc3codec/issues/10
Signed-off-by: Mariusz Skamra <c73850bd0bf85e95dce44c2ce1418ca55c1b6c5d@codecoup.pl>

google/liblc3,google/liblc3