driver: add SWDP driver interface API and bit-bang driver

Add Serial Wire Debug Port interface driver API and bit-bang driver.

The driver requires a simple Hardware Interface Circuits (HICs),
where signals CLK, DOUT, DIN, ENn, OE_ENn, RESETn
are connected to board GPIOs and buffered signals SWD_CLK and SWD_DIO
to the target.

Signal OE_ENn controls the direction of the Serial Wire (SWD_DIO),
ENn the buffers SWD_CLK possibly others and enables/disables HIC.

Signed-off-by: Johann Fischer <j.fischer@phytec.de>
Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>