* dac: move helpers to separate cpp and h
(cherry picked from commit aee71931db269fc256ab43e1fb84b71c77e215d7)
* dac: HAL_USE_DAC guards
(cherry picked from commit 5517844e4d0f79c7cf8c5bb097c110541063bddf)
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Co-authored-by: Andrey Gusakov <dron0gus@gmail.com>