sparc64: perf: make sure we do not set the 'picnht' bit in the PCR

sparc64: perf: make sure we do not set the 'picnht' bit in the PCR

Testing with the perf_fuzzer tool revealed an issue when the 'picnht' bit
was set in the Performance Control Register. Setting this bit means that
privileged software cannot access the PIC counter and we eventually end up
with messages of the form shown below, being reported.

NMI watchdog: BUG: soft lockup - CPU#788 stuck for 23s! [perf_fuzzer:336548]

This commit fixes the issue my making sure that the 'picnht' bit
is always reset when writing to the PCR register.

Orabug: 24926097

Signed-off-by: Dave Aldridge <david.j.aldridge@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>