adiv6: stay in same AP during dap_lookup_cs_component()

adiv6: stay in same AP during dap_lookup_cs_component()

Configuration file can specify, as target's debug AP, an AP that
contains a ROM table that points, in turn, to other APs.
Current code in cortex_a and aarch64 is not able to handle a
return from dap_lookup_cs_component() that points to another AP.

While it could be interesting to specify 'root' as target's debug
AP, drop any found value if it's not in the starting AP.

Change-Id: Id206e4fa7a29e9402c8e2393026817b410bbb8bd
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6826
Tested-by: jenkins