MIPS: Add Cavium OCTEON processor CSR definitions

Here we define the addresses and bit-fields of the Configuration and
Status Registers (CSRs) for some of the hardware functional units on
the OCTEON SOC.

Definitions are needed for:

CIU  -- Central Interrupt Unit.
GPIO -- General Purpose Input Output.
IOB  -- Input / Output {Busing,Bridge}.
IPD  -- Input Packet Data unit.
L2C  -- Level-2 Cache controller.
L2D  -- Level-2 Data cache.
L2T  -- Level-2 cache Tag.
LED  -- Light Emitting Diode controller.
MIO  -- Miscellaneous Input / Output.
POW  -- Packet Order / Work unit.

Signed-off-by: Tomaso Paoletti <tpaoletti@caviumnetworks.com>
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>