stlink: deprecate HLA support

stlink: deprecate HLA support

The STLink API that supports dap-direct is available from STLink
firmware v2j24, published in early 2015.
We can reasonably expect that any old STLink still in use today
has got at least one firmware update during the last 10 years.

Most of the board files in upstream OpenOCD still use the STLink
in HLA mode. This limits the test coverage of the dap-direct code,
which was introduced in OpenOCD v0.11.0.

- Rename interface/stlink.cfg as interface/stlink-hla.cfg to still
  provide support for HLA, adding a deprecated message.

- Rename interface/stlink-dap.cfg as interface/stlink.cfg to make
  dap-direct the default trasport.

- Add a redirect file interface/stlink-dap.cfg for users that have
  out-of-tree custom board files.

- Update all the board files to the new setup.

- Remove STLink HLA mentions from the documentation, while adding
  a reference to interface/stlink-hla.cfg

Checkpatch-ignore: LONG_LINE
Change-Id: I99366bb03cd3b83f8f408514e657f30e59813063
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8523
Tested-by: jenkins
Reviewed-by: Andrzej Sierżęga <asier70@gmail.com>