arm_adi_v5: describe Class 0x9 Device Architecture register

arm_adi_v5: describe Class 0x9 Device Architecture register

Use the list of values from ARM IHI0029E to decode and print the
Device Architecture register.
Add attribute 'unused' to the function, not used yet.

Change-Id: I7b1dd204bd1db671578c588372b667e23611876c
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6463
Tested-by: jenkins
Reviewed-by: Daniel Goehring <dgoehrin@os.amperecomputing.com>