[ARM] pxa: cpufreq-pxa2xx: allow frequency table selection

Following the removal of the "->policy" usage for PXA255 in patch
459fc208 (cpufreq: remove
policy->governor setting in drivers initialization), this patch
introduces an option (called "pxa255_turbo_table") to select either
the "run" or "turbo" frequency table.

It also cures the runtime warning that was printed each time the
frequency was changed.

Got rid of all references to CPUFREQ_POLICY_* for pxa255, and sticked
with the run/turbo thing.

Tested on an Arcom/Eurotech Viper.

Signed-off-by: Marc Zyngier <maz@misterjones.org>
Acked-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Eric Miao <eric.miao@marvell.com>