MIPS: Decouple BMIPS CPU support from bcm47xx/bcm63xx SoC code

BMIPS processor cores are used in 50+ different chipsets spread across
5+ product lines.  In many cases the chipsets do not share the same
peripheral register layouts, the same register blocks, the same
interrupt controllers, the same memory maps, or much of anything else.

But, across radically different SoCs that share nothing more than the
same BMIPS CPU, a few things are still mostly constant:

SMP operations
Access to performance counters
DMA cache coherency quirks
Cache and memory bus configuration

So, it makes sense to treat each BMIPS processor type as a generic
"building block," rather than tying it to a specific SoC.  This makes it
easier to support a large number of BMIPS-based chipsets without
unnecessary duplication of code, and provides the infrastructure needed
to support BMIPS-proprietary features.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: mbizon@freebox.fr
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Tested-by: Florian Fainelli <ffainelli@freebox.fr>
Patchwork: https://patchwork.linux-mips.org/patch/1706/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>