adapter: expose HLA interface in struct adapter_driver

adapter: expose HLA interface in struct adapter_driver

The transition of STM8/SWIM out of HLA will require a new struct
swim_ops in struct adapter_driver.
To simplify the development, make the HLA interface temporarily
accessible through the struct adapter_driver.
This commit will be reverted after the swim rework.

Change-Id: I1e4f370cf64641164d7bcaa22f75ac58c9240052
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5527
Tested-by: jenkins