selftests/thermel/intel: Add test to read power floor status

Some SoCs have firmware support to notify, if the system can't lower
power limit to a value requested from user space via RAPL constraints.

This test program waits for notification of power floor and prints. This
program can be used to test this feature and also allows other user space
programs to use as a reference.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>