cpufreq: longhaul: Make array speeds static const

Don't populate the read-only array speeds on the stack but instead
make it static. Also makes the object code a little smaller. Replace
hard-coded loop array bounds with ARRAY_SIZE.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>