jtag/xds110: switch to command 'adapter serial'

jtag/xds110: switch to command 'adapter serial'

The driver xds110 defines the command 'xds110 serial' to specify
the serial string of the adapter.

Remove and deprecate the driver command, and use 'adapter serial'.

Note: the original command 'xds110 serial' used a complex and
undocumented conversion of the serial number through multibyte
string, wide-character string and C cast. The XDS110 I can access
and the lsusb dumps available through Google don't show any
exotic USB serial that require such conversion. The original
developer doesn't remember any constraint that mandates such
conversion (see comments in https://review.openocd.org/4322/).
The conversion is removed by this patch.

Change-Id: I38909918079b2c1797ad85ebec2fea1b33743606
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6655
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins