ARM: stub out read_cpuid and read_cpuid_ext for CPU_CP15=n

Traditionally for !CPU_CP15 read_cpuid and read_cpuid_ext returned the
processor id independent of the parameter passed in. This is wrong of
course but theoretically this doesn't harm because it's only called on
machines having a cp15.

Instead return 0 unconditionally which might make unused code paths be
better optimizable and so smaller and warn about unexpected usage.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Message-Id: 1359646587-1788-2-git-send-email-u.kleine-koenig@pengutronix.de