PCMCIA: soc_common: convert to a stand alone module

Convert soc_common.c to be a stand alone module, rather than wrapping
it up into the individual SoC specific base modules.  In doing this,
we need to add init/exit functions for soc_common to register/remove
the cpufreq notifier.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>