driver: swdp_bitbang: rework pin configurations

Move low-level GPIO functions to a separate file and use GPIO driver
API if low-level GPIO support is not available for the platform.
Allows alternative pin configuration using only two pins, clk and dio.
Improve binding description.

Signed-off-by: Maximilian Deubel <[email protected]>
Signed-off-by: Johann Fischer <[email protected]>

Author: maxd-nordic

drivers/dp/Kconfig

@@ -24,6 +24,7 @@ config SWDP_BITBANG_DRIVER
 	bool "Serial Wire Debug Port bit-bang driver"
 	default y
 	depends on DT_HAS_ZEPHYR_SWDP_GPIO_ENABLED
+	depends on GPIO
 	help
 	  Serial Wire Debug Port bit-bang driver.