perf/uapi: Define PERF_MEM_SNOOPX_PEER in kernel header file

PERF_MEM_SNOOPX_PEER is defined only in tools uapi header. Although
it's used only by perf tool, not defining it in kernel header can
create problems in future.
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220928095805.596-8-ravi.bangoria@amd.com

include/uapi/linux/perf_event.h

@@ -1356,7 +1356,7 @@ union perf_mem_data_src {
 #define PERF_MEM_SNOOP_SHIFT	19
 
 #define PERF_MEM_SNOOPX_FWD	0x01 /* forward */
-/* 1 free */
+#define PERF_MEM_SNOOPX_PEER	0x02 /* xfer from peer */
 #define PERF_MEM_SNOOPX_SHIFT  38
 
 /* locked instruction */