turris-omnia-mcu-interface.h: Move command execution function to global header

Move the command execution functions from the turris-omnia-mcu platform
driver private header to the global turris-omnia-mcu-interface.h header,
so that they can be used by the LED driver.

Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://lore.kernel.org/r/20241111100355.6978-2-kabel@kernel.org


Signed-off-by: Lee Jones <lee@kernel.org>