perf: stop deadlock when cpu_up fails

When an attempt is made to free an event on a CPU which is
no longer online, perf tries to bring the CPU online. This
can fail, resulting in an UP_CANCELLED notifier, which
eventually tries to acquire the ctx->mutex which is already
being held by the cpu_up code.

Removing the attempt to bring the cpu up will remove this
deadlock, but also requires temporarily removing support of
counting events across hotplug. This will be restored in a
later patch.

CRs-fixed: 912295
Change-Id: Iaafa3c6688d26508857472fd5bb32139a137880e
Signed-off-by: Neil Leeder <nleeder@codeaurora.org>