cpu-hotplug: Keep atleast 1 online and un-isolated CPU

The PM_QOS_CPU_DMA_LATENCY vote attached to an IRQ is discarded,
if it is affined to an isolated CPU. So we need atleast 1 CPU
in online and un-isolate state. The scheduler rejects isolating
a CPU if it is the only online and un-isolated CPU in the system.
Add the same check for CPU hotplug.

Change-Id: I5bdfe6e3bb0352ed3ae5a2de90097b73d248f3fc
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>