drivers/swd: add support for SWD multidrop

drivers/swd: add support for SWD multidrop

According to ARM IHI0031C+ chapter 2.3.11 "TARGETSEL, Target Selection register"
multidrop capable DPv2 must not drive SWDIO line during the response phase
of a write to TARGETSEL register.

Introduce helper functions swd_cmd_returns_ack() and swd_ack_to_error_code()
to centralize these tests from all drivers to one place.

Introduce distinct error codes for SWD protocol.

Partly inspired by Graham Sanderson's http://review.openocd.org/4935

Change-Id: Ie5f9edb22e066a933a534bf2b29e7e1d3087dad1
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/6699
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins