jlink: change prototype of show_config*() functions

jlink: change prototype of show_config*() functions

To prepare for handling TCL return values consistently, all calls
to command_print/command_print_sameline should be ready to switch
to CMD as first parameter.

Change prototype of show_config*() functions to pass CMD instead
of CMD_CTX.

This change was part of http://openocd.zylin.com/1815 from Paul
Fertser and has been extracted and rebased to simplify the review.

Change-Id: I131a904774bf60ad1bf9d90dbc65927c246ac23a
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5080
Tested-by: jenkins