tty/8250_dw: Add support for OCTEON UARTS.

tty/8250_dw: Add support for OCTEON UARTS.

A few differences needed by OCTEON:

o These are DWC UARTS, but have USR at a different offset.

o OCTEON must have 64-bit wide register accesses, so we have OCTEON
  specific register accessors.

o No UCV register, so we hard code some properties.

Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-mips@linux-mips.org
Cc: Jamie Iles <jamie@jamieiles.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: http://patchwork.linux-mips.org/patch/5506/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>