KX165: Implement "direct tune mode"

[hbeni]

As per manual (p. 3-2):

The operating frequency can also be entered by accessing the
ACTIVE ENTRY (direct tune) mode which is done by pushing and holding the COMM TRANSFER
button for 2 or more seconds. In the direct tune mode, only the active part of the display is visible.
The desired frequency can be directly entered into the display. Push the COMM TRANSFER but-
ton again to return to the active/standby display.

Same is true for the NAV frequency (p. 3-3).

This is implemented in the ADF already, I think, so we can peek there