ARM: uniphier: rework SMP code to support new System Bus binding

During the review process of the UniPhier System Bus driver
(drivers/bus/uniphier.c), the current binding of the System Bus
Controller turned out to be no good.  In order to use the driver,
some nodes in the device trees must be tweaked.  It would also have
impacts on the SMP code because the SMP related registers are
located in the System Bus Controller block.  This commit reworks
the smp_operations to support the new binding, but still supports
the old binding, too.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>