ARM: 7847/1: mcpm: Factor out logical-to-physical CPU translation

This patch factors the logical-to-physical CPU translation out of
mcpm_boot_secondary(), so that it can be reused elsewhere.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>