perf: stop deadlock if attempt to bring 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 code, which brings up the CPU.

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.

Conflicts:
	kernel/events/core.c
	kernel/events/hw_breakpoint.c

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