powerpc/perf: Revert to original NO_SIPR logic

This is a revert and then some of commit 860aad71 "Add regs_no_sipr()".
This workaround was only needed on early chip versions.

As before NO_SIPR becomes a static flag of the PMU struct.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>