On ADIv6 the system root ROM table is found by reading the DAP DP
registers BASEPTR0 and BASEPTR1.
Add option 'root' to the commands 'dap info' to let it retrieve
the system root ROM table's AP from DAP DP, then use such AP for
following dump.
Change-Id: I1789457a005faa3870c5d14f763378d2f6a5f095
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6462
Tested-by: jenkins