adi_v5: use macro DP_APSEL_MAX to allocate struct adiv5_ap

adi_v5: use macro DP_APSEL_MAX to allocate struct adiv5_ap

Commit 11019a824d02 ("adi_v5: enforce check on AP number value")
introduces the macro DP_APSEL_MAX and use it in place of hardcoded
magic numbers for the upper limit of AP selection value.

Use the macro also while defining the array of struct adiv5_ap in
struct adiv5_dap.

Change-Id: I88f53ceb710f92a48a8026a365709fbf2d9e6912
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5806
Tested-by: jenkins