switch to use libfirmware timer

[mck1117]

Current issue:

Why is this here, instead of util.mk?

[rusefillc]

I assume that timer.cpp assumes some "abstract" methods are implemented by the consumer.

In order for consumers to have an option not to use timer.cpp and thus not implement dependencies it's currently not in util.mk

I am open to all improvements! At the moment I believe the consumers of libfirmware are ECU, WBO, GDI4 and stim.