powercap/intel_rapl: Simplify rapl_find_package()

Simplify how the code to discover a package is called.  Rename
find_package_by_id() to rapl_find_package_domain()

Syntax only, no functional or semantic change.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-pm@vger.kernel.org
Link: https://lkml.kernel.org/r/ae3d1903407fd6e3684234b674f4f0e62c2ab54c.1557769318.git.len.brown@intel.com