[CPUFREQ] use an enum for speedstep processor identification

The "unsigned int processor" everywhere confused Rusty, leading to
breakage when he passed in smp_processor_id().

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>