perf/x86/intel: Move BTS index to 47

The bit 48 in the PERF_GLOBAL_STATUS is used to indicate the overflow
status of the PERF_METRICS counters.

Move the BTS index to the bit 47.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200723171117.9918-5-kan.liang@linux.intel.com