target/armv8: Handle instruction cache invalidate

target/armv8: Handle instruction cache invalidate

Some armv8 target have separate i-cache and d-cache.
The actual code only handles the flush of the d-cache.

Change-Id: I61a223b43c71646bbbed8fa63825360c67700988
Signed-off-by: Adrien Grassein <agrassein@nanoxplore.com>
Signed-off-by: Adrien Charruel <acharruel@nanoxplore.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8655
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins