arm: mvebu: avoid hardcoded virtual address in coherency code

Now that the coherency_get_cpu_count() function no longer requires a
very early mapping of the coherency unit registers, we can avoid the
hardcoded virtual address in coherency.c. However, the coherency
features are still used quite early, so we need to do the of_iomap()
early enough, at the ->init_timer() level, so we have the call of
coherency_init() at this point.

Unfortunately, at ->init_timer() time, it is not possible to register
a bus notifier, so we add a separate coherency_late_init() function
that gets called as as postcore_initcall(), when bus notifiers are
available.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>