swd_gpio.cpp: add debug print

Signed-off-by: Federico Vaga <federicov@linino.org>
swd_gpio.{h|cpp}: add code to reset SW-DP

Signed-off-by: Federico Vaga <federicov@linino.org>
swddude.cpp: set CLK and DIO GPIO

Signed-off-by: Federico Vaga <federicov@linino.org>
swd_gpio.{cpp|h}: implement read operation

Signed-off-by: Federico Vaga <federicov@linino.org>