perf core: Allocate perf_buffer in the target node memory

I found the ring buffer pages are allocated in the node but the ring
buffer itself is not.  Let's convert it to use kzalloc_node() too.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210315033436.682438-1-namhyung@kernel.org