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