drivers/jlink: Print serial numbers when multiple devices are connected

drivers/jlink: Print serial numbers when multiple devices are connected

When multiple jlink programmers are connected and no specific serial
or USB location is specified, print out the detected serial numbers.

Signed-off-by: Marcus Nilsson <brainbomb@gmail.com>
Change-Id: I280da2b85363f7054c5f466637120427cadcf7d1
Reviewed-on: https://review.openocd.org/c/openocd/+/8356
Reviewed-by: Mark Zhuang <mark.zhuang@spacemit.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins