The IRQ operation(enable/disable) should be avoided when throttling is
controlled via PTC method. It is replaced by the migration of task.

This fixes an oops on T61 -- a regression due to
f79f06ab b/c FixedHW support tried to read remote MSR with interrupts disabled.
Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>