oprofile: Fix usage of CONFIG_HW_PERF_EVENTS for oprofile_perf_init and friends

The implementations are flagged in Makefile with CONFIG_HW_PERF_EVENTS
instead of CONFIG_PERF_EVENTS.

Cc: stable@kernel.org # 37.x
Signed-off-by: Ari Kauppi <kauppi@papupata.org>
Signed-off-by: Robert Richter <robert.richter@amd.com>