x86 thermal: Disable power limit notification interrupt by default

The package power limit notification interrupt is primarily for
system diagnosis, and should not be blindly enabled on every
system by default -- particuarly since Linux does nothing in the
handler except count how many times it has been called...

Add a new kernel cmdline parameter "int_pln_enable" for situations where
users want to oberve these events via existing system counters:

$ grep TRM /proc/interrupts

$ grep . /sys/devices/system/cpu/cpu*/thermal_throttle/*

https://bugzilla.kernel.org/show_bug.cgi?id=36182

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>