RP2350: Improve config examples for secure/non-secure debug

[PetteriAimonen]

This replaces the previous examples rp2350-dbgkey-nonsecure.cfg and rp2350-dbgkey-secure.cfg that had a hardcoded sequence of bits being sent. The new file rp2350-dbgkey.cfg can take the key from a variable. It also adds a print of the lock status after the key has been sent.

Example usage:

$ openocd -f interface/cmsis-dap.cfg -c 'set DEBUGKEY {0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00}' -f rp2350-dbgkey.cfg 
Open On-Chip Debugger 0.12.0+dev-00559-g04154af5d (2024-04-15-14:10)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
Warn : An adapter speed is not selected in the init scripts. OpenOCD will try to run the adapter at very low speed (100 kHz).
Warn : To remove this warnings and achieve reasonable communication speed with the target, set "adapter speed" or "jtag_rclk" in the init scripts.
Info : Using CMSIS-DAPv2 interface with VID:PID=0x2e8a:0x000c, serial=E660443043813128
Info : CMSIS-DAP: SWD supported
Info : CMSIS-DAP: Atomic commands supported
Info : CMSIS-DAP: Test domain timer supported
Info : CMSIS-DAP: FW Version = 2.0.0
Info : CMSIS-DAP: Interface Initialised (SWD)
Info : SWCLK/TCK = 0 SWDIO/TMS = 0 TDI = 0 TDO = 0 nTRST = 0 nRESET = 0
Info : CMSIS-DAP: Interface ready
Info : clock speed 100 kHz
Info : SWD DPIDR 0x4c013477
Warn : gdb services need one or more targets defined
Core 0 CSW value: 0x02000052 (secure debug: denied, non-secure debug: allowed)
Core 1 CSW value: 0x02000012 (secure debug: denied, non-secure debug: denied)
Now attach a debugger to your RP2350 and load some code

Another file rp2350-nonsecure.cfg can be used to connect to targets which only allow non-secure debugging.

(This pull request is related to issue #129)

[PetteriAimonen]

(On second thought, it might even be possible to combine this all in rp2350.cfg. It could automatically send the debug key if a variable is defined. It could also detect if secure debug is available and choose the mode based on it.)

[P33M]

I probably should have read this PR before banging my head against tcl in P33M@a2e24ea.

This is a workable implementation - but please fold into the base rp2350.cfg. In effect the user should invoke openocd with -c "set DBGKEY {bytes}" -c "set NSDEBUG 1" -f target/rp2350.cfg or similar. Also, if a debug key isn't defined, then a default shouldn't be transmitted to the RP-AP.