[trace][intelpt] Support system-wide tracing [8] - Improve the single buffer...

[trace][intelpt] Support system-wide tracing [8] - Improve the single buffer perf_event configuration

We were setting some events to be written in the data buffer of the
perf_event, but we don't need that.

Besides that, we don't need the data buffer to be larger than 1, so we
can reduce its size.

Differential Revision: https://reviews.llvm.org/D125850