transport: use a bitmask for the transport

transport: use a bitmask for the transport

Move the transport's names in a local array in the transport
framework.

Replace the string struct transport::name, that identifies the
transport, with a bitmask where each bit corresponds to one of the
available transports.

Change-Id: I6bdf7264d5979c355299f63fcf80bf54dcd95cee
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8674
Tested-by: jenkins
Reviewed-by: zapb <dev@zapb.de>