target: allow moving and resizing working area on running target

target: allow moving and resizing working area on running target

target configure -work-area-xxx calls target_free_all_working_areas()
and sets the desired new parameter. Without this change the working area
does not get reallocated if it has been allocated before.
target_free_all_working_areas() results in work area containing one block
marked as free.

Completely free working area in target_free_all_working_areas()

Change-Id: I79c681082f32f2a96a2b40eb3b8751e427549693
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4797
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>