x86, bts, ptrace: move BTS buffer allocation from ds.c into ptrace.c

Impact: restructure DS memory allocation to be done by the usage site of DS

Require pre-allocated buffers in ds.h.

Move the BTS buffer allocation for ptrace into ptrace.c.
The pointer to the allocated buffer is stored in the traced task's
task_struct together with the handle returned by ds_request_bts().

Removes memory accounting code.

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -1168,6 +1168,10 @@ struct task_struct {
 	 * This field actually belongs to the ptracer task.
 	 */
 	struct bts_tracer *bts;
+	/*
+	 * The buffer to hold the BTS data.
+	 */
+	void *bts_buffer;
 #endif /* CONFIG_X86_PTRACE_BTS */
 
 	/* PID/PID hash table linkage. */