ARM: Perfevents: Make L2 Cycle counter raw code consistent

The L2 cycle counter is a different counter than the one used
for counting L1 cycles but they shared the same raw code,
0xff only to be differentiated by the PMU_TYPE_SHARED identifier.

perf stat -e rsff counted L2 cycles
perf stat -e rff counted L1 cycles

Keep the raw event code for the two separate.
0xfe for L2 cycles reduces chances of counting the wrong
thing accidently.

Signed-off-by: Ashwin Chaugule <ashwinc@codeaurora.org>