arm_adi_v5: add/move apsel member in struct adiv5_dap

arm_adi_v5: add/move apsel member in struct adiv5_dap

This patch tries to make some order in "apsel" mess.
"dap apsel" command was quite useless (and broken) by itself.
With this patch we can use it to select between AHB or APB memory access
(previous patch 05ab8bdb813acdcd74afa71d6656c2df816cb230 was somehow broken).

- moves member apsel (in struct adiv5_dap) to ap_current
- adds apsel member

this strange choice is made trying to keep coherence in "dap apsel" command
 and to keep compatibility with other code (for example cortex_a8).

Signed-off-by: Luca Ellero <lroluk@gmail.com>